Modifying a television signal to inhibit recording/reproduction

ABSTRACT

A composite television signal is modified to inhibit the reproduction of an unauthorized recording thereof by conventional video recorders but enable the display of a video picture therefrom on a television receiver. The length of a frame (more particularly, the length of each field in a frame) is increased or decreased from standard length, either by changing the time duration of the respective horizontal line intervals included in each frame while keeping a constant, standard (e.g. 525) number of lines per frame, or by changing the number of horizontal line intervals which constitute a frame while maintaining the standard duration of each line interval (e.g. 63.5 microseconds). A profile pattern representing the variation of the video frame duration, or vertical period, (whether by changing the horizontal line durations or the number of lines in a frame) with respect to time is adjustable to correspondingly control the rate at which the vertical period (i.e. frame length) changes, the maximum and minimum vertical period and the ratio of increased to decreased vertical periods. Accordingly, substantially the same electronics responsive to the profile pattern may be used to modify the television signal; and the profile pattern itself may be changed easily, such as by simple software modifications, to accommodate different circumstances and to satisfy different conditions.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for modifying acomposite television signal to inhibit reproduction of an unauthorizedrecording thereof by conventional video recorders but enable the displayof a video picture therefrom on a television receiver; and, moreparticularly, to a technique by which the vertical periods, i. e. thelengths of successive frames, of the television signal are varied underthe control of a "profile pattern" which may be easily adjusted so as tocorrespondingly adjust the manner in which the vertical period changes.

With the abundance of video tape recorders (VTR's) now in use in manyhomes, it has become commonplace for users to record off-the-airtelevision programs for subsequent, and often repeated, viewing. Inaddition, consumers have enthusiastically accepted pre-recorded videoprogramming, typically, commercially successful motion pictures; andthis has resulted in large libraries of pre-recorded video tapes forsale or rent to the public. While such legitimate recordings arewelcomed, the financial profit associated with selling or rentingpre-recorded video tapes has given rise to illegal piracy. So-calledvideo tape pirates reproduce several, often hundreds of unauthorizedcopies of a video tape, thereby depriving the rightful owners ordistributors of lawful income.

Television subscription networks, such as so-called sattelite or cabletelevision distribution systems, face similar difficulties. To preventadequate reception by non-subscribers, such television subscriptionnetworks typically encode, or "scramble", the distributed televisionsignals, thereby defeating acceptable video displays of those televisionsignals by non-subscribers who are not provided with proper decoders or"descramblers". However, a subscriber may simply connect a videorecorder to his decoder so as to record for subsequent and repeatedviewing a desired video program that is distributed over thesubscription network. Such recording for later viewing decreases themarket interested in a re-distribution of that video program over thesubscription network. As this market decreases, individuals mayterminate their subscriptions and the video program distributor (i. e.the cable network) may suffer financial damage.

Providers of subscription television programming have long proposedso-called "pay per view" broadcasting. This broadcasting contemplates aonce-only distribution of valued video programming, such as first-runmotion pictures, highly popular sporting events, special entertainmentevents, and the like, to subscribers who would be charged a one-time feeto receive that video program. Such one-time broadcasting is quitesensitive to video recording which, if permitted, would seriously erodethe value of pay-per-view transmission.

Analogous to pay-per-view video distribution is the so-called"electronic theater". As presently envisaged, the electronic theaterwould be quite similar to a typical motion picture theater, except thatactual prints or copies of a motion picture need not be used in eachtheater. Rather, high resolution television signals can be broadcastsimultaneously to several theaters, such as by satellite transmission,for "real time" display to the theater audience. However, the success ofthe electronic theater may be contingent, in part, on the ability toprevent unauthorized recording and video tape duplication of thebroadcast program.

Of course, scrambling or encoding of a video signal prevents anon-subscriber from recording the video program. However, an authorizedsubscriber or one who obtains a compatible descrambler may use his VTRto record the descrambled video program. It is preferred that the basictelevision signal be modified to the extent that even afterscrambling/descrambling an acceptable video picture may be reproduced ona conventional television receiver, but the operation of a VTR should bedefeated such that it cannot be used to record and reproduce asatisfactory video picture.

One technique proposed for making a television signal nonrecordablerelies upon the automatic gain control (AGC) circuitry normally includedin a VTR. A large pulse is inserted into the vertical blanking intervalto "confuse" the AGC circuitry into substantially attenuating the videosignal during recording, thereby making it quite difficult to reproducea video signal of adequate level. It is believed that this proposal canbe easily defeated and, thus, it does not adequately inhibit a VTR fromrecording and playing back the modified television signal. It also isbelieved that this technique will defeat the operation of certainaddressable "descramblers" used in some cable systems, resulting in anunsatisfactory video picture ultimately displayed on a subscriber'stelevision receiver.

Another technique for modifying a television signal to prevent itsrecording/reproduction relies upon the relative sensitivity of thevertical synchronizing signal detecting circuitry normally provided invirtually all VTR's. By removing a portion of the vertical synchronizingpulses included in the vertical blanking interval, the verticalsynchronizing signal detector included in most VTR's will be unable todetect those vertical sync pulses, resulting in loss of critical servocontrol information needed for proper operation of the VTR. Since thevertical synchronizing circuitry included in most television receiversis not as sensitive, there is no loss of vertical synchronization in thetelevision receiver. Recently, however, the vertical synchronizingsignal detecting circuitry included in VTR's has been significantlyimproved, and in some instances digital techniques have been used,resulting in the ability of such VTR's to record and reproducetelevision signals that have been modified as aforesaid.

Various other proposals have been made regarding modification of thevertical synchronizing signal for the purpose of defeating the verticalsync locking circuitry normally provided in VTR's. Some proposals havesuggested that some of the horizontal synchronizing signals be deletedfrom the transmitted television signal; but these suggestions aresubject to the same difficulties associated with video signal scramblingtechniques: one who has a descrambler or decoder may record thetelevision signal.

One technique which may offer the promise of success contemplates achange in the length of the two video fields which constitute a frame oftelevision signals. U. S. Pat. Nos. 4,488,176 and 4,673,981 both suggestthat the frame length may be enlarged or reduced by adding orsubtracting horizontal line intervals to each frame. Thus, the framelength varies from its nominal 33.33 milliseconds, depending upon thenumber of lines which have been added to or deleted from the videoframe. In both proposals, however, the rate at which lines are added toand deleted from the frames is fixed, and over a period of time thenumber of lines which are added is equal to the number of lines whichare deleted. Furthermore, in both proposals, the duration of eachhorizontal line interval is fixed at the standard 63.5 microsecondduration.

OBJECTS OF THE INVENTION

Therefore, it is an object of the present invention to provide animproved technique for modifying a composite television signal so as toinhibit that signal from being adequately recorded/reproduced from a VTRbut enable the display of a video picture therefrom on a televisionreceiver.

Another object of this invention is to provide a technique for varyingthe vertical periods of a television signal, either by varying thenumber of horizontal line intervals included in each frame or by varyingthe duration of the respective line intervals in that frame.

A further object of this invention is to provide a technique of theaforementioned type wherein the vertical period is varied in accordancewith a "profile pattern" which represents the manner in which thevertical period varies over time.

It is an additional object of this invention to provide a technique asaforementioned wherein the profile pattern is adjustable so as toprovide a dynamic variation in the vertical period and therebyaccommodate various conditions, restrictions and limitations of theparticular television signal broadcast/transmission or supply systemwith which the modified television signal is used.

Still another object of this invention is to provide a technique asaforementioned, wherein the profile pattern is varied to assure thatvirtually all types of VTR's are inhibited from adequately recording andreproducing the modified television signal.

Yet a further object of this invention is to provide a technique asaforementioned, wherein the profile pattern is selected and/or modifiedto minimize perturbations in the video picture displayed by varioustypes of television receivers.

Yet another object of this invention is to provide a technique asaforementioned wherein the profile pattern preferably is selected toprovide transitions in the pattern through a level corresponding to astandard vertical period substantially at changes in the scene of thetelevision picture.

A still further object of this invention is to provide a technique asaforementioned wherein the profile pattern can be shifted to modify themaximum and minimum vertical periods, the rate at which the verticalperiod changes, and the ratio between greater and lesser verticalperiods.

It is an additional object of this invention to provide a technique asaforementioned that can be used in a subscription television network.

Another object of this invention is to provide a technique for insertinginto a predetermined portion of at least one field in each frameinformation for controlling the vertical period of that frame,transmitting the television signal containing this information to adistribution source, and then modifying the vertical period of thetelevision signal just prior to distribution.

Various other objects, advantages and features of the present inventionwill become readily apparent from the ensuing detailed description, andthe novel features will be particularly pointed out in the appendedclaims.

SUMMARY OF THE INVENTION

In accordance with this invention, a technique is provided for modifyinga composite television signal to inhibit reproduction of unauthorizedrecording thereof by conventional video recorders but enable the displayof a video picture therefrom on a television receiver. Stated otherwise,the television signal is effectively made nonrecordable. In oneembodiment, the time durations of horizontal line intervals included ina first predetermined number of frames of the television signal areincreased from a standard horizontal line duration to a pre-establishedmaximum time duration and then are decreased from the pre-establishedmaximum to the standard. Thereafter, the time durations of thehorizontal line intervals in a second predetermined number of frames aredecreased from the standard to a pre-established minimum time durationand then are increased from the pre-established minimum to the standard.The same number of horizontal line intervals is included in each frame,regardless of the vertical period which is increased or decreased as thetime durations of the horizontal line intervals are increased ordecreased.

In accordance with one aspect of this embodiment, the number of frameswhich contain increased horizontal line durations is equal to the numberof frames which contain decreased horizontal line durations. As afeature of this aspect, the difference between the standard horizontalline duration and the pre-established maximum time duration issubstantially equal to the difference between the standard horizontalline duration and the pre-established minimum time duration.

In accordance with another aspect of this embodiment, the number offrames which contain increased line durations differs from the number offrames which contain decreased line durations. Preferably, however, theintegral of the increased line durations over the first number of framesis substantially equal to the integral of the decreased line durationsover the second number of frames.

In accordance with yet another feature of this embodiment, the change inthe horizontal line durations over a period of time is represented as aprofile pattern, and this pattern is used to control the horizontal linedurations in respective frames. As one aspect, the profile pattern maybe modified to accommodate different conditions and circumstances,without requiring any significant change in the electronics used tomodify the television signal. Accordingly, the television signalrepresenting one complete television program may be modified inaccordance with several different profile patterns to inhibit differenttypes of video recorders (having different characteristics) fromreproducing satisfactory video pictures from the modified televisionsignal.

It is another feature of this embodiment that a change in the scene ofthe video picture represented by the television signal is detected, andthe profile pattern preferably crosses a level corresponding to the"standard" horizontal line duration at the scene change occurrences.

As another feature of this embodiment, the horizontal line intervals aredigitized and the digitized video signals are stored in respectiveaddresses of a memory device. The digitized video signals are read outat slower read-out rates to increase the horizontal line durations andat faster read-out rates to decrease the horizontal line durations. Theread-out rates are controlled by the profile pattern.

As yet another aspect of this embodiment, the digitized video signalsare geometrically corrected such that the first digitized activehorizontal video line interval which is read out from the memorycorresponds to the top raster line in a displayed video picturenotwithstanding the change in the duration of the read out line intervalfrom the standard line duration. Advantageously, the start times atwhich the digitized active video line intervals are read out from thememory are adjusted as a function of the profile pattern, whereby thestart time is delayed when the time durations are increased and thestart time is advanced when the time durations are decreased.

As a further feature, the digitized line intervals are comprised ofpixels, and a portion of the value of a pixel of one line interval iscombined with a portion of the value of an adjacent pixel in the nextline interval to produce a composite pixel value, these composite pixelvalues being stored as compensated digitized line intervals.

In accordance with another embodiment of this invention, the verticalperiod is increased by increasing the number of horizontal lineintervals included in a first predetermined number of frames so as toexceed a standard number of horizontal line intervals normally includedin a frame, and the vertical period is decreased by decreasing thenumber of horizontal line intervals included in a second predeterminednumber of frames so as to be less than the standard number. A profilepattern represents the rate at which the numbers of line intervals areincreased and decreased, the maximum and minimum number of lineintervals that may be reached in a frame and the numbers of framescontaining the increased and decreased numbers of line intervals.

Advantageously, scene changes in the video picture represented by thetelevision signal are detected, and the profile pattern preferablycrosses the level representing the "standard" number of horizontal lineintervals in a frame at, or just after, detected scene changes. Thisminimizes a viewer's perception of video picture perturbations that maybe attributable to changes in the vertical period from its nominalduration.

As one aspect of this embodiment, the profile pattern resembles atrapezoid waveform which crosses the standard number of line intervalsin a frame at those frames in which a scene change is detected. Otherprofile patterns, such as sinusoidal or rectangular, may be used.

As a feature of this embodiment, the profile pattern is selectivelychanged so as to correspondingly change one or more of the following:the rate at which the horizontal line intervals in a frame change, themaximum and/or minimum number of line intervals included in a frame, andthe number of frames containing more and/or less than the standardnumber of line intervals.

As another feature of this embodiment, different profile patterns arestored and those patterns which best defeat the record/playbackoperability of most VTR's are selected.

As another feature of this embodiment, an offset may be selectivelyadded to the profile pattern so as to "shift" that pattern up or downwith respect to the standard number of line intervals included in aframe, thereby changing the manner in which the vertical period isvaried without requiring a significant change or modification in theelectronics used to modify the television signal.

As another feature of this embodiment, each horizontal line interval isdigitized and written into a memory; and the profile pattern is used todetermine the number of line intervals in a frame which are read fromthat memory. Preferably, the stored line interval which is read out asthe first "active" line interval from the memory corresponds to the topvisible line in the video picture, and the profile pattern is used tochange the read-out time of that first active line to compensate forchanges in the vertical period. Since the active video line intervals ina video picture are substantially less than the line intervals in atelevision frame, "black" level video information is generated beforeand after the active line intervals read from the memory.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the present invention solely to the embodiment shownand described herein, will best be understood in conjunction with thefollowing drawings in which:

FIG. 1 is a block diagram representing the manner in which the verticalperiods (i. e. frame lengths) of a television signal are adjusted inaccordance with the present invention;

FIGS. 2A and 2B are graphical representations of profile patterns usedby the present invention;

FIGS. 3A-3C are graphical representations of the manner in whichvertical compensation in the video picture is attained when using-thepresent invention;

FIGS. 4A and 4B are diagrammatical representations which are useful inunderstanding the manner in which frame lengths are adjusted inaccordance with this invention;

FIG. 5 is a block diagram representing one manner in which geometriccompensation is achieved when using the present invention;

FIG. 6 is a block diagram of the electronics used to generate varioustiming signals for controlling frame length adjustments;

FIGS. 7A-7F are waveform diagrams which are useful in understanding theoperation of the electronics shown in FIG. 6;

FIG. 8 is a block diagram of electronics used to adjust frame lengths inaccordance with another embodiment of the present invention;

FIG. 9 is a block diagram of an overall television subscription systemin which the present invention finds ready application:

FIG. 10 is a logic diagram representing the manner in which"fingerprint" information may be provided in the system shown in FIG. 9to detect misappropriation of the television signal transmitted via thesubscription system;

FIGS. 11A-11G are waveform diagrams which are useful in understandingthe operation of FIG. 10;

FIG. 12 is a block diagram showing in greater detail a portion of thesystem shown in FIG. 9;

FIGS. 13A-13C are waveform diagrams which are useful in understandingone aspect of the subscription system shown in FIG. 9;

FIG. 14 is a block diagram showing in greater detail another portion ofthe system illustrated in FIG. 9;

FIG. 15 represents the manner in which the present invention may be usedin the system shown in FIG. 9;

FIG. 16 is a block diagram showing in greater detail yet another portionof the system shown in FIG. 9: and

FIG. 17 is a block diagram showing in greater detail the manner in whichvideo signals are written into and read from a memory to provide bothdescrambling and vertical period adjustment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals are usedthroughout, and in particular to FIG. 1, there is illustrated a blockdiagram of one embodiment of the present invention. The apparatusillustrated in FIG. 1 is adapted to modify the vertical period of atelevision signal so as to increase or decrease the vertical period withrespect to nominal field intervals of 16.683 milliseconds, therebydefeating the ability of virtually all commercially available VTR's torecord and satisfactorily reproduce a video picture from the modifiedtelevision signal. By adjusting the vertical period, either bymaintaining a constant number of horizontal line intervals but varyingthe duration of groups of those line intervals, or by adding or deletingline intervals while maintaining a constant duration of each lineinterval, the capstan and drum servo circuits normally provided in VTR'sare inhibited from operating satisfactorily. However, this verticalperiod adjustment does not prevent the vertical sync detecting circuitrynormally provided in most television receivers, including thosetelevision receivers recently introduced having digital synchronizingcircuitry, from displaying satisfactory video pictures. Thus, themodified television signal cannot be adequately recorded and reproduced,but nevertheless can be satisfactorily received for video picturedisplay on a conventional television receiver.

The system shown in FIG. 1 includes an analog-to-digital converter 102(referred to hereafter for convenience as an A/D converter), a memorydevice 104, memory write and read controls 106 and 108, a centralprocessor 110, a digital-to-analog converter 112 (referred to hereaftersimply as a D/A converter), a profile library 118 and a scene changedetector 120. A/D converter 102 is adapted to digitize a receivedtelevision signal such that pixels having respective pixel values areproduced to represent each horizontal line interval included in thereceived television signal. As will become apparent, it may not benecessary to digitize the synchronizing information included in thecomposite television signal and, therefore, A/D converter 102 may beadapted simply to digitize only the useful video information. Forexample, suitable timing signals may be generated and supplied to theA/D converter such that it operates only during those intervals thatuseful video information (also referred to herein as "active" videoinformation) is present. As an alternative, a synchronizing signalseparator circuit (not shown) may be provided to strip the usualhorizontal synchronizing signals (including the usual color burstsubcarrier signal) from the composite television signal, therebysupplying A/D converter 102 only with useful video information.

The A/D converter is coupled to memory 104 which, preferably, comprisesan addressable memory adapted to store the pixels included in at leasteach active horizontal line interval that has been digitized by A/Dconverter 102. For convenience, memory 104 may be thought of as beingformed of addressable rows, with each row being adapted to store thepixels which constitute an active horizontal line interval (e.g. lineintervals 21 to 241 of a field). Write control circuit 106 and readcontrol circuit 108 are coupled to memory 104 and serve to generatewrite and read addresses, respectively, as well as timing and othercontrol signals, whereby each line interval may be written into and readfrom a row of memory 104. As illustrated, write and read controlcircuits 106 and 108 are coupled to processor 110 and receive addressand other control signals from the processor. Thus, the processor isadapted to determine the particular addresses of memory 104 in whichdigitized horizontal line intervals are stored and from which thosedigitized line intervals are read. As will be described, each lineinterval, and preferably each active line interval, is written intomemory 104 at a substantially constant, standard write-in ratesynchronized with the usual horizontal line frequency f_(H) of 15.735KHz; and in one embodiment, read control circuit 108 is adapted to readout from memory 104 each digitized active line interval at a variableread-out rate within a predetermined range determined by processor 110.In one embodiment, the read-out rate may vary from approximately 15.370KHz to approximately 16.110 KHz. These ranges are not intended to belimitations but, rather, should be viewed merely as illustrative andexplanatory of the present invention.

Since each frame of television signals is comprised of alternating fieldintervals, one being designated an "odd" field and the other beingdesignated an "even" field, it is preferable that memory 104 be thoughtof as including two field memories, one for the odd field and one forthe even. Thus, when pixels are written into the odd memory, the pixelswhich are stored in the even memory may be read out therefrom.Conversely, after pixels have been read from the even memory, the lineintervals contained within the next even field are written into thiseven memory, and the pixels now stored in the odd memory are read out.

As a further refinement, it is appreciated that, since the rate at whichline intervals are read out from memory 104 differs from the rate atwhich line intervals are written in, it is possible that a field of lineintervals may not have been fully read from the field memory at the timethat the next field is to be written therein. To accommodate thispossibility, memory 104 may be formed of an array of eight memories,such as four memory storage devices to accommodate four odd fields andfour memory storage devices to accommodate four even fields. It shouldbe recognized that these numerical examples merely are illustrative andare not intended to limit the present invention solely thereto. Anydesired number of odd and even field memories may be used to carry outthe present invention. With multiple field memories, it is appreciatedthat the write and read address signals generated by write and readcontrol circuits 106 and 108 in response to processor 110 include memoryselect signals such that the appropriate but different field memoriesare selected for concurrent write-in and read-out operations, asdetermined by the processor. By using multiple field memories, thepossibility of data "collisions" caused by overwriting data into a fieldmemory which has not been fully read out is minimized.

As a still further refinement of memory 104, this memory may be thoughtof as three separate but substantially identical memory devices, one foreach color component normally included in the composite televisionsignal. More particularly, since a composite television signal iscomprised of red (R), green (G) and blue (B) components, memory 104 maybe thought of as being formed of R, G and B memory devices, each memorydevice being comprised of multiple (e. g. eight) field memories.Consistent with this concept of R, G and B memories, A/D converter 102may be thought of as being comprised of R, G and B A/D converters. Sincethe television signal supplied to the A/D converter typically is in NTSCformat, an NTSC-to-RGB decoder may be provided (not shown) to separatethe received composite television signal into its three color componentsand to supply these color components to the R, G and B A/D converters,respectively. The output of memory 104, which is understood to comprisethe outputs of the field memories and, if separate RGB memory devicesare used, the outputs of the field memories included in each of the RGBmemory devices, is coupled to D/A converter 112. For the embodimentwherein separate RGB memory devices are used, D/A converter 112 may bethought of as being comprised of separate R, G and B D/A converters.

The D/A converter is adapted to convert the digitized pixel values to ananalog signal, thus effectively recovering the original usefulinformation contained in the original television signal, with newvertical timing determined by the read-out rate provided by read controlcircuit 108. Thus, the D/A converter reconstructs the originaltelevision signal, but with increased or decreased horizontal lineinterval durations, as will be further described.

D/A converter 112 is coupled to a mixer 114 which also is coupled to asynchronizing signal generator 116. The mixer functions to insert theusual horizontal and vertical synchronizing signals, burst signals andequalizing pulses conventionally used in NTSC format, as well as the"non-active" line intervals (e.g. lines 1 to 20 and 242 to 262 of afield). The output of the mixer thus comprises the modified televisionsignal containing the original video information but with lengthened orshortened vertical periods, depending upon whether the horizontal lineintervals in the respective fields have been increased or decreased.This modified television signal then may be transmitted to conventionaltelevision receivers which, notwithstanding the changed verticalperiods, reproduce an accurate video picture. However, if this modifiedtelevision signal is supplied to a conventional VTR, the changedvertical periods inhibit that VTR from recording and accuratelyreproducing an acceptable video picture. Hence, unauthorized productionof video tapes is effectively prevented.

Processor 110 is coupled to profile library 118 which comprises astorage device, such as a read only memory (ROM) that stores profiledata representing the manner in which the vertical periods arelengthened or shortened over a period of time. Profile datacorresponding to several different profiles are stored in profilelibrary 118, and processor 110 is adapted to select a desired one ofthose profiles for controlling the operation of read control circuit108. As an example, the profile data establishes the duration of eachline interval in a particular frame. For instance, the profile data mayestablish the duration of the horizontal line intervals for the firstframe to be 63.56 microseconds, whereas the duration of the horizontalline intervals in, for example, frame #16 may be 65.03 microseconds.Likewise, the profile data may establish the duration of the lineintervals included in frame #78 to be 62.10 microseconds. Of course, theline durations of the various frames therebetween and thereafter alsoare established by this profile data. Thus, when a particular frame ofthe television signal is received, the read-out rate associated withthat frame is determined by the selected profile, and the duration ofthe line intervals included in that frame is set accordingly.

Processor 110 also is coupled to time code reader/generator 122. In oneapplication of the present invention, the source of the televisionsignal supplied to the illustrated apparatus comprises a video recorderwhich, as is known, includes a time code reader for reading the timecode normally recorded on the video tape. Thus, when a video recorder isused as the source of the television signal, a time code identificationof each reproduced frame may be provided to accompany that frame.However, if the source of the television signal is other than a videorecorder, or if the time code is not present, it is desirable toidentify each frame of that television signal. Consequently, a time codeframe identification for each frame is generated by time codereader/generator 122. It is appreciated, therefore, that the time codereader/generator serves to supply processor 110 with an identificationof each frame in the received television signal. This frameidentification information is used by processor 110 in conjunction withthe profile data retrieved from profile library 118 to control thereading out of line intervals from memory 104.

The present invention serves to increase and decrease the lengths offrames included in the television picture over a period of time. As willbe described, the frame lengths are changed either by changing thedurations in the line intervals included in each frame, thus increasingor decreasing the overall time duration of the frame, or by adding ordeleting line intervals to the frame. From observation andexperimentation, when either embodiment is adopted, visual perturbationsand interference in the video picture which eventually is displayed willbe minimized if changes in the lengths of frames pass through "standard"lengths (e. g. 16.683 milliseconds) when (or just after) changes in thetelevised scene are detected. For this reason, and as will be describedin greater detail below, scene change detector 120 is coupled toprocessor 110 to apprise the processor of the particular frame in whicha scene change is detected.

The detection of a scene change may be carried out by using conventionaldevices, such as Oak Communications, Inc. video scene change detectorModel CTV 0725, or other circuitry which may detect, for example, asignificant difference in the overall luminance level of one field orframe relative to that of a preceding field or frame. Other techniquesknown to those of ordinary skill in the art may be used to detect ascene change. From experience, it has been found that, in a typicalprogram created specifically for television broadcasting, a scene changeoccurs on the average of once every five seconds.

It is desirable to provide a supervisory override to a programmed changein the vertical period at certain conditions. For example, if the videopicture corresponding to the television signal to be modified includes apattern of horizontal lines, such as a video picture wherein venetianblinds constitute a prominent portion, changes in the vertical periodduring such frames may result in a noticeable disturbance in the videopicture. In those instances, it is preferred to reduce deviations in thevertical period from the standard 16.683 milliseconds until a frame isreached that is substantially free of such horizontal lines. Thereafter,the programmed vertical period changes may continue. However, thestandard vertical period is retained for only a relatively few frames toprevent those television receivers having digitized synchronizingcircuitry from "locking" onto the standard vertical period, and therebybecoming unable to "follow" subsequent changes in the vertical period.

In this regard, a monitor 126 is coupled to receive and display thetelevision signal and a supervisory control 128 is coupled to processor110 to permit a supervisor to supply a signal to the processor forhalting continued changes in the vertical period. The supervisorycontrol may include a keyboard or other input device by which anappropriate signal may be supplied through the processor. It isappreciated that other characteristics of the video picture may resultin noticeable interference if the vertical period corresponding to thatpicture is changed. Supervisory control 128 thus provides a manualoverride to vertical period changes when the supervisor observes suchpicture content.

The operation of the television signal modifying apparatus shown in FIG.1 now will be described with reference to two embodiments: one whereinthe vertical period is changed by varying the durations of the lineintervals included in each frame; and the other wherein the verticalperiod is changed by adding or deleting line intervals to or from theframe. In the first embodiment, although the horizontal timing ischanged, the number of line intervals included in each frame is fixed.In the other embodiment, the number of line intervals included in eachframe is varied, but the duration of each line interval remains fixed.

Both embodiments operate in conjunction with the profile data stored inprofile library 118. As mentioned above, the profile data represents themanner in which the vertical period changes over a period of time. Agraphical representation of the profile pattern corresponding to theprofile data stored in profile library 118 is represented by thewaveforms shown in FIG. 2A. Merely as an example, four separate profilepatterns 202, 204, 206 and 208 are illustrated, and each of thesepatterns broadly resembles a trapezoidal waveform, although otherwaveforms, such as sinusoidal or rectangular, may be used. The ordinateof FIG. 2A represents the vertical period, either in terms of the totalnumber of lines included in a frame or the average duration of each lineinterval within that frame, and the abscissa represents time. It will beappreciated that the abscissa also represents the particular frame ofthe television signal, such as identified by time code reader/generator122. Thus, the profile patterns shown in FIG. 2A represent the length ofeach frame and further indicate that the frame lengths vary relative tothe standard length of 525 lines (or the standard horizontal lineinterval of 63.53 microseconds).

From profile pattern 202, it is seen that the vertical period of themodified television signal increases from the standard length to alength equal to 537 lines (or a length formed of 525 lines, each havingan average line interval duration of 65.01 microseconds). Thereafter,the vertical period remains at this maximum level for a predeterminednumber of frames, whereafter the vertical period decreases toward thestandard length and then is reduced below that length toward a minimumvertical period shown as 513 lines (or a minimum length formed of 525lines each having an average line interval duration of 62.10microseconds). The vertical period then remains constant for anotherpredetermined number of frames, whereafter the vertical period increasesfrom its minimum length (513 lines) towards its standard length. Profilepatterns 204, 206 and 208 are similar but, as is readily apparent,exhibit markedly different characteristics. In the examples shown, theprofile patterns may vary, one from the other, with respect to the rateat which the vertical period increases or decreases with respect totime, the total number of frames having greater than standard length,the total number of frames having less than standard length and themaximum and minimum frame lengths. The illustrated profile patterns arecomprised of positive and negative portions, the positive portion ofeach representing those frames having greater than standard verticalperiod and the negative portion of each representing those frames havingless than standard vertical period. It has been found that if the areaunder the curve corresponding to the positive portion, shown as area A,is equal to the area under the curve of the negative portion, shown asarea B, there is no net increase or decrease in vertical period and,therefore, there is no net delay or advance in the overall verticalperiod. Furthermore, it is preferred that the area A (as well as thearea B) be such that the capacity of memory 104 is not exceeded, i.e.the accumulated delay between read-out and write-in does not exceed thestorage space of the memory, so that a frame of video information is notdropped.

In profile pattern 204, although the total number of frames havingincreased vertical period is seen to be less than the total number offrames having decreased vertical period, and although the maximumincrease in the vertical period is seen to be greater than the maximumdecrease in vertical period, nevertheless the area A' under the positiveportion of profile pattern 204 is substantially equal to the area B'under the negative portion of this profile pattern. Likewise, the areaA" under the positive portion of profile pattern 206 is equal to thearea B" under the negative portion of this profile pattern. Also, thearea A'" under the positive portion of profile pattern 208 is equal tothe area B'" under the negative portion of this profile pattern. That isthe integral of the increased vertical period over those frames havinggreater than standard frame length is substantially equal to theintegral of the decreased vertical period over those frames having lessthan standard frame length. Thus, notwithstanding the marked differencesin the illustrated profile patterns, by reason of these equal positiveand negative areas (or integrals), the overall timing of the verticalperiod, averaged over time, is approximately "standard", therebyminimizing accumulated delays and avoiding sound/videomis-synchronization.

Desirably, the selected profile pattern should cross the abscissa at thetime of occurrence of a scene change in the video picture. This isbecause maximum perturbation in the video picture generally will occurduring this transition between maximum and minimum levels in the profilepattern but such perturbation will not be noticed by a typicaltelevision viewer if a scene change also occurs at (or just prior to)that time. By providing an inventory of profile patterns in profilelibrary 118, the particular pattern providing a "best fit" toaccommodate detected scene changes may be selected to control the mannerin which the vertical period is changed. It is expected that scenechanges of a television program may occur with varying frequency; andprocessor 110, upon detecting changes in the frequency of occurrence ofscene changes, selects a more appropriate profile pattern to satisfy the"best fit" objective. Furthermore, some television receivers may exhibitinstability if the maximum or minimum vertical period is maintained formore than a few (e.g. 100-200) frames, and the processor selects profilepatterns that reduce the possibility of such instability yet defeat thesatisfactory operation of conventional VTR's. It is appreciated,therefore, that the selection of the profile pattern to be used tocontrol changes in the vertical period may vary while processing thetelevision signal.

Additionally, in the event that some VTR's nevertheless operateadequately while the vertical period varies under the control of aparticular profile pattern, a pattern may be selected from profilelibrary 118 which, from experience, is known to defeat the successfuloperation of even those VTR's. Hence, from time to time, processor 110selects that profile pattern for controlling the vertical periodadjustment operation; thereby minimizing perturbations in video picturedisplay while maximizing nonrecordability of the television signal.

Still further, if the present invention is used in conjunction with asubscription television distribution network, such as shown in thesystem diagram of FIG. 9, certain constraints and restrictions may beimposed upon the selection of the profile pattern, depending upon theoperating characteristics of the television distribution network. Forexample, the subscription encoding/scrambling circuitry may limit theminimum number of line intervals included in a frame. If this minimumnumber is greater than the minimum number of lines established by, forexample, profile pattern 202, then profile pattern 204 or profilepattern 208 may be substituted. Profile library 118 thus accommodatesthe constraints imposed by the particulars of the televisionsubscription network with which the present invention may be used.

Another technique for accommodating the aforementioned constraint whichmay limit the minimum (or maximum) number of line intervals included ina frame is represented by offset adjustment control 124, and is depictedin FIG. 2B. The offset adjustment control serves to add an offset to theprofile data, thereby effectively raising or lowering the profilepattern with respect to the abscissa. FIG. 2B represents profile pattern202 with a negative offset added thereto, thereby resulting in aneffective "lifting" of the profile pattern. This offset may be achievedby, for example, adding a predetermined number of lines (e. g. 2, 4, 6,etc. lines) to the profile data included in a selected profile.

Although the profile patterns shown in FIGS. 2A and 2B are illustratedas relatively smooth curves having progressively increasing anddecreasing leading and trailing edges, it is contemplated that abruptchanges (e.g. spikes) may be provided in the patterns, whetherintentional or inadvertent.

Briefly, in operation, a received television signal, which may besupplied from a video recorder or from conventional television signalgenerating or transmitting apparatus, is digitized by A/D converter 102to produce pixels having respective pixel values over the active videoportion of each line interval. Successive lines of pixels in eachreceived video field are written into a field memory included in memory104 under the control of write control circuit 106. As mentioned above,the pixels are written into the memory at a standard, fixed ratesynchronized with the normal horizontal synchronizing frequency f_(H).As one field of pixels is written into memory 104, a preceding field ofpixels is read from the memory under the control of read control circuit108. In one embodiment, the rate at which the pixels are read from thememory is varied, as represented by the profile patterns shown in FIG.2A, under the control of processor 110. A profile pattern stored inprofile library 118 is selected as aforesaid, and this selected profilepattern thus controls the increase and decrease in the rate at which thelines of pixels are read from memory 104. It is seen that, as theread-out rate increases, the duration of the line interval of pixelsread from a row of memory 104 is reduced. Conversely, as the read-outrate decreases, the duration of this line interval increases.

Preferably, the read-out rate and, thus, the duration of each lineinterval is not changed. Rather, the read-out rate is changed once everytwenty-five line intervals. Furthermore, this read-out rate is increasedor decreased by about 8 nanoseconds for each change in the read-outrate. As a result, the duration of the line intervals included in afield changes by approximately 100 nanoseconds from the beginning to theend of that field. It has been found that a change in the line durationof 100 nanoseconds over a video field interval will not disturb orinterfere with the normal video display of a television receiver. Thus,the length of each frame may increase or decrease by approximately 200nanoseconds from its preceding frame.

Time code reader/generator 122 identifies for processor 110 each framethat is received. By comparing the actual frame count of the receivedtelevision signal with the frame count included in the profile patternselected from profile library 118, processor 110 supplies read controlcircuit 108 with read-out data which establishes the proper read-outrates for the line intervals included in that frame. Thus, each line ofpixels is read from memory 104 with a line duration determined by theselected profile pattern; and these pixels are reconverted into ananalog video signal by D/A converter 112. Nevertheless, these analogvideo signals now exhibit the line durations which have been determinedby the selected profile.

Mixer 114 adds to the active video signals supplied by D/A converter 112the usual horizontal synchronizing signals, burst signals, equalizingpulses, vertical synchronizing pulses and non-active horizontal lineintervals. The reconstituted but modified television signal then istransmitted from the mixer.

As scene changes in the received television signal are detected by scenechange detector 120, processor 110 determines which of the profilepatterns stored in profile library 118 constitute the "best fit" to theoccurrences of those scene changes. Should a different profile patternbe found to provide this best fit, processor 110 selects that newprofile pattern for controlling the operation of read control circuit108. Furthermore, the processor periodically selects a profile patternknown to defeat the operability of virtually all conventional VTR's, aswell as a profile pattern that will not result in the "lock up" oftelevision receivers having digital synchronizing circuitry, asmentioned above.

The received television signal also is displayed on monitor 126. If asupervisor observes that the video picture contains components whichwill result in visual interference if the vertical period correspondingto that video picture is changed, the supervisor may override theaforedescribed vertical period adjustment operation. In that event, nodeviations from "standard" are made to the vertical period, that is, nochanges are made in the read-out rate, until the supervisor determinesthat such interference in the video picture no longer will be present.Changes in the read-out rate then may resume.

In the alternative embodiment, the rate at which line intervals ofpixels are read from memory 104 remains constant. However, the number oflines included in a frame is increased or decreased, as represented bythe profile patterns shown in FIGS. 2A and 2B. The particular address ofmemory 104 which is selected for a read-out operation is, of course,determined by read control circuit 108 under control of processor 110.The profile pattern establishes the number of the lines included in eachframe read from memory 104, and processor 110 advantageously varies thestart time at which the first line of active video information is readfrom memory 104 by read control circuit 108.

In the event that the profile pattern calls for the number of linesincluded in a frame to be greater than the standard number (e. g.greater than 525 lines), processor 110 commands synchronizing signalgenerator 116 to continue to generate non-active (or "black") horizontalline intervals which are supplied by mixer 114 as the output TV signal;and the processor also commands read control circuit 108 to delay thetime at which the stored lines of active video information are read fromthe memory. Hence, although the same number of active lines are includedin the output TV signal, the total number of lines therein is greaterthan the standard number because synchronizing signal generator 116supplies "extra" black lines. Alternatively, if less than the standardnumber of lines is to be included in a frame, thereby reducing the framelength, processor 110 interrupts the generation of black horizontal lineintervals by synchronizing signal generator 116, and concurrentlyadvances the time at which read control circuit 108 reads the storedlines of active video information from memory 104.

It will be appreciated that as the period of each field intervalincreases and decreases, whether by changing the number of linesincluded in a frame or by changing the duration of the line intervals ina frame, a vertical shift is imparted into the video picture which isdisplayed from the modified television signal. For example, and withreference to the embodiment wherein the vertical period is changed bychanging the number of lines included in the frame, the line intervalwhich typically is displayed as the first raster line of the videopicture, that is, the line interval which constitutes the top of thevideo picture, usually is line interval #21. If the vertical period isincreased (i. e. if the frame length is increased), line interval #21,if read out at the same time as normally read in a vertical period ofstandard length, will not be displayed as the first raster line (i.e. asthe top line). Rather, a later line interval, for example, line interval#22, now would constitute the first raster line of the displayed videopicture. Conversely, if the vertical period is decreased, line interval#21, if read out at the same time as normally read in a vertical periodof standard length, may constitute the second or third raster line ofthe video picture; and a preceding line interval, such as line interval#20 now would constitute the first raster line of the video picture. Theforegoing is graphically represented in FIGS. 3A-3C.

To compensate for this vertical shift in the position of the top line ofthe video picture, processor 110 controls read control circuit 108 toadvance or delay the time at which it addresses the row of memory 104 inwhich line interval #21, the first active line of the video picture, isstored. Thus, when the vertical period is increased, as shown in FIG.3B, read control circuit 108 addresses memory 104 to read out at a latertime (Δt) the row in which the pixels of line interval #21 are stored.Conversely, if the vertical period is decreased, as shown in FIG. 3C,read control circuit 108 addresses memory 104 to read out at an earliertime (Δt) the row in which the pixels of line interval #21 are stored.Thus, the read address is controlled such that the row read from memory104 which contains the first raster line in the video picture is delayedor advanced depending upon whether the vertical period is increased ordecreased, respectively. As a numerical example, line interval #21 mayread from the memory at the time when line interval #24 normally isread, in the event that the vertical period is increased (FIG. 3B); andline interval #21 may be read from the memory at the time when lineinterval #18 normally is read, in the event that the vertical period isdecreased (FIG. 3C).

In describing the operation of the apparatus illustrated in FIG. 1, ithas been assumed that memory 104 is comprised of several field memorydevices. As represented diagrammatically in FIGS. 4A and 4B, lines ofpixels are written into the field memories during a time duration T andare read from those field memories over another time duration T'. It isrecognized that these time durations T and T' normally are not equalbecause the read-out duration is increased or decreased to change thevertical period, as discussed above.

In the representation of FIGS. 4A and 4B, it is assumed that immediatelyafter a field memory is filled, or loaded, it is unloaded. However, adelay in the unloading of a memory may be provided, for example, fourfield memories may be loaded before the first field memory is unloaded.Processor 110 is adapted to determine when a particular field memoryselected for a loading operation has not yet been fully unloaded. Whenthat occurs, the incoming field, and more particularly, the incomingframe, simply is discarded. If FIG. 4A represents the field memorieswhich are loaded and FIG. 4B represents the field memories which areunloaded, it is seens that the nth unload cycle of field memory A endsjust as, or slightly later than, the time at which this very same fieldmemory is to be loaded for the (n+1)th time. This overlapping of theloading and unloading of the very same field memory could result ininterference and, therefore, processor 110 simply discards the fieldswhich otherwise would have been loaded into field memories A and Bduring this (n+1) th cycle.

The number of memory load (and unload) cycles which can be executedbefore a data collision occurs, that is, before the very same fieldmemory is selected for loading before it has been fully unloaded, may bedetermined as follows: Let N be the number of such memory load cyclesthat may be carried out before a data collision occurs. That is, N isthe number of memory load cycles which may be carried out before anincoming frame of video information must be dropped. Then:

T=the duration needed to load a field memory.

T'=the duration needed to unload a field memory.

P=T/T'.

M=the number of field memory devices (in the present example, M=8).

N=(P +1)/M(P-1)-1/(P-1).

A modification in the apparatus illustrated in FIG. 1 is contemplated.As described above, scene change detector 120 operates concurrently withthe loading of memory 104; and as mentioned above with respect to FIGS.4A and 4B, a field memory is unloaded immediately after it has beenloaded. Processor 110 selects a profile pattern from profile library 118to best fit the scene changes detected by scene change detector 120. Inthe event that additional time is needed for processor 110 to select theappropriate profile pattern, suitable delays may be imparted, wherenecessary. For example, several field memories may be loaded before thefirst field memory is unloaded. As a further alternative, the televisionsignal may be supplied to scene change detector 120 while itconcurrently is recorded. Then, the recorded television signal may beplayed back to A/D converter 102 for loading into memory 104. Theinherent delay provided in recording and then reproducing the televisionsignal should accommodate any time delays needed to detect scene changesand select the appropriate profile patterns for controlling the framelength of the modified television signal.

For the embodiment wherein the vertical period is changed by changingthe line interval durations therein, both horizontal and verticalgeometric distortions in the video picture may result. This is becausethe vertical distance traversed by the slight slant of each horizontalraster line varies if the horizontal line duration varies. As the lineduration increases so too does the vertical distance traversed by thisraster line. Conversely, as the line duration decreases, the verticaldistance covered by the slight slant of this line also decreases. It hasbeen found that geometric correction generally is not needed for thosefields in which the ratio P (discussed above with reference to FIGS. 4Aand 4B) is approximately unity. However, as P increasingly deviates fromunity, that is, as the profile pattern approaches its maximum andminimum levels, distortion compensation is appropriate.

FIG. 5 is a block diagram representing one embodiment by which geometriccompensation is effected for the embodiment wherein the vertical periodis varied by changing the durations of the horizontal line intervals.This compensation arrangement is comprised of field memories 402 and404, field memories 416 and 418, look up tables 410 and 412, a tableaddress generator 408 and an adder 414. Field memories 402, 404, 416 and418 may be viewed collectively as an embodiment of memory 104 (FIG. 1).Field memories 402 and 404 are adapted to receive the line intervals ofpixels produced by the A/D converter, and the addresses in which theselines of pixels are stored are determined by memory read/write controlcircuit 406. As an example, field memory 402 is adapted to store theline intervals of an odd field and field memory 404 is adapted to storethe line intervals of an even field. The output of field memory 402 iscoupled to look up table 410 and the output of field memory 404 iscoupled to look up table 412.

Each of the look up tables stores data representing differentproportions of pixel values. To provide geometric compensation, aportion of a pixel in one line interval is added to another portion of apixel in the next adjacent line interval (i.e. the line intervaladjacent thereto in the video display), and the resultant reconstitutedpixel is used as a replacement for the original. Depending upon theparticular location in the profile pattern, these proportions vary. Theparticular pixel read from field memory 402 constitutes a portion of theaddress for look up table 410, and the particular present location inthe profile is used to generate another portion of this look up tableaddress. Table address generator 408 is coupled to receive profile datafrom processor 110 and to generate address data corresponding to thepresent location on the profile pattern. In response to the addressesrepresented by table address generator 408 and the pixel values suppliedby field memory 402, the proportion of the pixel value stored in theaddressed location of look up table 410 is read out and supplied toadder 414.

Similarly, look up table 412 is coupled to field memory 404 and to tableaddress generator 408 and serves to supply to adder 414 the proportionstored in the location then being addressed. It is appreciated that thelook up tables may comprise read only memory devices.

Adder 414 is adapted to combine the proportions of pixel values suppliedthereto by look up tables 410 and 412 to produce a re-valued pixel. Theadder is coupled to field memories 416 and 418 which function as odd andeven field memories, respectively, to store the re-valued pixelstherein. Although not shown, it will be appreciated that the lineintervals of re-valued pixels stored in field memories 416 and 418 areread out under the control of read control circuit 108 in the mannerdiscussed above. Hence, memories 416 and 418 may be thought of as arraysof memories similar to the arrays described above for memory 104 (FIG.1). The outputs of field memories 416 and 418 are coupled to D/Aconverter 422 which reconstructs a compensated analog video signal whosevertical interval has been increased or decreased in accordance with theselected profile pattern.

A start read control circuit 420 also has been provided for the purposeof adjusting the start time at which a line of pixels stored in memory416 or 418 is read out. Start control circuit 420 is coupled to fieldmemories 416 and 418 and is responsive to the profile data suppliedthereto by processor 110 to determine the start time at which therespective line intervals are read from these field memories. As will beappreciated, the start time is advanced (i.e. it is generated earlier inthe read cycle) when the durations of the line intervals are increasedand the start time is delayed when the durations of the line intervalsare decreased.

In operation, digitized line intervals of the television signal, moreparticularly, the pixels which constitute the active video portion ofeach line interval, are supplied to field memories 402 and 404. Memoryread/write control 406 selects one of the field memories to storesuccessive line intervals during the reception of one field, and thenthe other field memory is selected to store the line intervals includedin the next-following field. For example, an odd field of line intervalsis stored in field memory 402 and then the next-following even field ofline intervals is stored in field memory 404. Although only two fieldmemories are illustrated, it will be appreciated that eight fieldmemories may be used to accommodate the eight fields included in foursuccessive frames.

After field memories 402 and 404 are loaded, they are unloaded byreading out the line intervals stored therein. Preferably, each pixel inthe line interval is read out in succession. Of course, the particularlocation on the profile pattern at the time a field memory is unloadedis known from the profile pattern supplied to table address generator408. Depending upon the profile data supplied to the table addressgenerator, an address signal is generated and applied to look up tables410 and 412. In addition, as a pixel is read out of field memory 402,its pixel value is supplied to look up table 410 and constitutes anotherportion of the table address. Thus, the combination of the pixel valueand profile data is used to address look up table 410 which, in turn,supplies to adder 414 data representing a particular portion, orpercentage, of the pixel value read out from field memory 402.

At the same time that a line interval is read out of field memory 402, aline interval which would be displayed as the next adjacent line in thevideo picture produced in response to the contents of field memories 402and 404 is read from field memory 404. The read out timing of the fieldmemories is such that, when a particular pixel is read from field memory402, the pixel in the next adjacent line interval which lies, forexample, directly below this pixel, is read from field memory 404. Thispixel value read from field memory 404 constitutes a portion of theaddress of look up table 412, and the table address which had beengenerated by table address generator 408 in response to the profile datasupplied thereto is used as another portion of the address for look uptable 412. Hence, data is supplied from look up table 412 to adder 414which represents that portion or percentage of the pixel value read fromfield memory 404 as determined by the present location along the profilepattern as represented by the profile data supplied to table addressgenerator 408.

Adder 414 adds that portion of the pixel data read from field memory 402to that portion of the pixel data read from field memory 404 to producea "corrected" value of the pixel read from field memory 402. Thiscorrected value is stored in field memory 416 in the same location asthe original pixel occupied in field memory 402. Thus, the originalpixel value is replaced by the corrected pixel value.

This same operation is carried out when the next pixels are read fromfield memories 402 and 404 until field memory 416 is supplied with aline interval of corrected pixel values. Then, the next line intervalstored in field memory 402 is read out, and a portion of each pixelvalue in that line interval is added to a determined portion of eachpixel value in the line interval re-read from field memory 404. As aresult, adder 414 produces "corrected" pixel values for the lineinterval now read from field memory 404; and these corrected pixelvalues now are stored in field memory 418 in the same location as theoriginal pixels occupied in field memory 404.

As a numerical explanation, let it be assumed that line 55 of fieldmemory 402 and line 56 of field memory 404 are read out (it isrecognized that the lines of the odd and even fields are interlaced).Let it be further assumed that each line interval contains approximately900 pixels. Now, as an example, when pixel 150 of line 55 is read fromfield memory 402, pixel 150 is read from line 56 of field memory 404.Look up table 410 supplies a percentage of the value of pixel 150 fromline 55 and look up table 412 supplies a percentage of the value ofpixel 150 from line 56. Adder 414 adds the percentage of the value ofpixel 150 from line 55 to the percentage of the value of pixel 150 fromline 56 to produce a "corrected" value for pixel 150 of line 55. Thiscorrected value of pixel 150 in line 55 is written into field memory 416at the proper location in the row in which line 55 is stored. Thisoperation continues until field memory 416 stores a "corrected" field ofpixels.

Next, line interval 57 is read from field memory 402 and line 56 isre-read from field memory 404. When, for example, pixel 150 of line 57is read from field memory 402, look up table 410 is addressed to supplyto adder 414 a percentage of the value of pixel 150. Likewise, whenpixel 150 of line 56 is read from field memory 404, look up table 412 isaddressed to supply to adder 414 a percentage of the value of thispixel. Adder 414 combines the percentages of the values of pixel 150from lines 57 and 56, respectively, to produce a "corrected" pixelvalue. This corrected value of pixel 150 is stored in field memory 418at line 56 and, thus, replaces the original value of pixel 150 from line56 read from field memory 404.

From the foregoing, it is seen that corrected odd and even fields arestored in field memories 416 and 418, respectively, thereby providinggeometric compensation to distortions which otherwise may arise when thevertical period is increased or decreased by increasing or decreasingthe durations of the line intervals included therein.

It is recognized that, as the duration of a line interval increasesbeyond standard, that is, a line interval greater than 63.56microseconds, the first pixel which corresponds to the left edge of thevideo picture corresponding to that line interval is effectively"shifted" to the right. To place this first pixel at the left edge ofthe video picture, the start time at which this line interval is readfrom field memory 416 (or field memory 418) should be shifted to theleft. Stated otherwise, the start time at which the line interval beginsto be read out of the field memory should be advanced relative to a"standard" start time. Conversely, if the duration of the line intervalis decreased below standard, the first pixel in the displayed portion ofthis line interval is effectively shifted to the left. To repositionthis pixel of the shortened line interval at the left edge of the videopicture, the start time at which this line interval is read out from thefield memory should be delayed relative to the standard start time.Horizontal start control circuit 420 is responsive to the profile datasupplied from processor 110 to advance or delay the start time forreading out each line interval stored in the field memories. As theprofile pattern increases, that is, as the time durations of the lineintervals are increased, horizontal start control circuit 420 advancesthe start time for reading from the field memories by a correspondingamount. Conversely, when the profile pattern decreases, thereby reducingthe durations of the horizontal line intervals, the horizontal startcontrol circuit delays the start time for reading from the fieldmemories. Consequently, distortions that otherwise might appear in thevideo picture are compensated, particularly distortions that would bemost visible in displayed vertical lines.

In the embodiment shown in FIG. 5, it has been preferred to utilize lookup tables 410 and 412 to determine percentages of pixel values inaccordance with the present location of the profile pattern during thevertical period adjustment operation. As an alternative, a multipliercircuit can be used, wherein the value of a pixel read from field memory402 (or field memory 404) is multiplied by a factor which varies as theprofile pattern varies. As a result, a percentage of the pixel value isproduced; and this percentage may be combined with the percentage of thevalue of an adjacent pixel in the next line to provide a corrected pixelvalue.

Referring now to FIG. 6, there is illustrated a block diagram ofapparatus used to control the reading out of memory 104 (or the readingout of field memories 416 and 418) by which the vertical period isadjusted by changing the durations of the horizontal line intervalsincluded in the frames. The apparatus includes a latch circuit 602, acounter 604, latch circuits 610 and 612, a counter 614, a comparator608, latch circuits 618 and 620 and a comparator 616. Latch circuit 602is adapted to receive data representing the duration of a line interval,as determined by the profile pattern. This data may be derived directlyfrom the profile data and, as an example, may represent a line durationwithin the range of 62.10 microseconds to 65.03 microseconds. Latchcircuit 602 is coupled to counter 604 and is adapted to preset thecounter to a count representing the profile-determined duration of theline interval.

Counter 604 is coupled to a clock circuit 606 which, as a numericalexample, may generate clock pulses of a frequency 120 MHz. Counter 604is adapted to be decremented in response to the clock pulses to producean output pulse HCLR, representing the end of the line interval whoseduration is represented by the count to which the counter has beenpreset. The output of counter 604 is coupled to counter 614, and thepulses HCLR are supplied to counter 614 as clock pulses.

Latch circuit 610 is adapted to store therein the number of the firstline interval whose duration is t. Latch circuit 612 is adapted to storethe number of the last line interval having this duration t. It will beappreciated that the duration t is equal to the duration supplied tolatch circuit 602. The outputs of latch circuits 610 and 612 are coupledto one input of comparator 608, and the comparator includes anotherinput coupled to the output of counter 614. An output of comparator 608is coupled to latch circuit 602 and functions as an enable, or load,input.

Latch circuit 618 is adapted to receive and store data representing thedelay or advance (Δt) for reading out the line interval whichconstitutes the first viewable line of the video picture (e.g. line#21). From the foregoing discussion of FIGS. 3A-3C, it is appreciatedthat, depending upon the increase or decrease in the vertical period,the read-out time of the line (e.g. line #21) which constitutes the topof the video picture may vary. In the above-discussed example, the firstline of the video picture has been assumed to be line 21 for "standard"vertical periods, and the read-out time of line #21 is delayed forincreased vertical periods and is advanced for decreased verticalperiods.

Latch circuit 620 is adapted to receive data representing the number ofthe bottom-most viewable line of the video picture, typically line #241.The latch circuits are coupled to one input of comparator 616, and thiscomparator includes another input coupled to counter 614. The output ofcomparator 616 is coupled to a flip-flop circuit 622 which, as will bedescribed, toggles between set and reset states in response to theoutput of the comparator. The output of flip-flop circuit 622, forexample, the SET output thereof, is coupled to one input of an AND gate624 whose other input is coupled to a flip-flop circuit 630 to receive arectangular signal, designated HDSP, which coincides with the activeportion of a horizontal line interval.

A look up table 626 is coupled to latch circuit 602 to receive as anaddress the data representing the duration of a line interval, asdetermined by the profile pattern. Look up table 626 stores countnumbers representing different line interval durations. A particularduration count is read from the look up table to a counter 628 to presetthat counter. Counter 628 is coupled to clock circuit 606 and, inaccordance with one example described herein, is adapted to decrementits count in response to each clock pulse supplied thereto. The counterincludes "count A" and "count B" outputs coupled to the set and resetinputs, respectively, of flip-flop circuit 630.

The manner in which the timing circuit illustrated in FIG. 6 operatesnow will be described in conjunction with the waveforms shown in FIGS.7A-7F. FIG. 7A represents the horizontal line intervals of a typicaltelevision signal, including a horizontal synchronizing pulse, a burstsignal and active video information. It is appreciated that theseparation of the horizontal synchronizing pulses increases if theduration of the line interval increases and, conversely, the separationbetween horizontal synchronizing pulses decreases as the duration of theline interval decreases.

The duration of the line interval being read from memory 104 (or fromfield memories 416 and 418) is supplied to and stored in latch circuit602. The data supplied to all of the illustrated latch circuits may beprovided by processor 110 (FIG. 1).

Counter 604 is preset to a count corresponding to thisprofile-determined duration, and the count is decremented in response tothe clock pulses supplied to counter 604 by clock circuit 606. As anexample, counter 604 may be preset to a count of 7625 when the durationof the line interval being read from the memory is the standard duration(e. g. approximately 63.56 microseconds). The counter may be preset to acount of 7450 when the duration of the line interval is to be, forexample, 62.10 microseconds, and the counter may be preset to a count of7800 when the duration of the line interval is to be, for example, 65.03microseconds. It is appreciated that, as the preset count of counter 604increases, the period required for the counter to be fully decrementedlikewise increases.

Counter 604 produces the pulse HCLR, shown in FIG. 7B, when it is fullydecremented. At that time, the HCLR pulse is used as a load pulse toload the counter with a preset count received from latch circuit 602 andrepresenting the duration of the next line interval to be read from thememory. This HCLR pulse also is supplied to counter 614 whereat it iscounted, and the HCLR pulse also functions as a load pulse to loadcounter 628 with a count read from look up table 626 in response to datarepresenting the duration of the next line interval, as received fromlatch circuit 602.

Counter 614 initially is reset by a pulse UNEND which, as one example,may be generated upon detecting the first set of equalizing pulsesnormally included in a field of the television signal. FIG. 7Drepresents these equalizing pulses, together with the usual set ofvertical synchronizing pulses, followed by another set of equalizingpulses and horizontal blanking pulses normally provided in the verticalblanking interval of a television signal. FIG. 7D also illustratestypical horizontal synchronizing pulses included in, for example, lineintervals 20-262 of a typical field. FIG. 7E represents the UNEND pulseswhich generally coincide with the beginning of the first set ofequalizing pulses included in a field. As an alternative, it will beappreciated that the UNEND pulses may be generated by counter 614 aftera predetermined number of HCLR pulses (e. g. 262 or 263 HCLR pulses)have been counted.

The count of counter 614 represents the number of the line intervalbeing read from the memory. Stated otherwise, the count of counter 614represents the vertical line count. This vertical line count is comparedby comparator 608 to a count stored in latch circuit 610 representingthe number of the first line interval having the duration represented bythe data stored in latch circuit 602. It is recalled that, preferably, aset of twenty-five line intervals is provided with the same duration,and the number of the twenty-fifth line interval is supplied to latchcircuit 612. When this last line interval having the durationrepresented by the data stored in latch circuit 602 is reached,comparator 608 produces an output to enable latch circuit 602 to storedata representing the duration of each line interval included in thenext set of twenty-five line intervals. From the foregoing discussion,it is appreciated that the duration t changes from one set oftwenty-five line intervals to the next set by approximately 8nanoseconds. Thus, the data stored in latch circuit 602 will increase ordecrease by 8 nanoseconds at each latch-load cycle.

The vertical line count produced by counter 614 is compared bycomparator 616 to a count representing the top viewable line of thevideo picture, as stored in latch circuit 618 (e.g. line #21), and alsoto a count representing the bottom viewable line of that video picture,as stored in latch circuit 620 (e.g. line #241). When the vertical lineis equal to the top line, for example, when the vertical line count isequal to line 21, comparator 616 sets flip-flop circuit 622 whichsubsequently is reset when the vertical line count is equal to the lastline of the video picture, for example, when it is equal to line 241.FIG. 7F represents the output of flip-flop circuit 622. The negativeportion of the illustrated rectangular waveform coincides with thevertical synchronizing interval included in a field of the televisionsignal, and the positive portion of this rectangular waveform representsthe viewable portion of the television signal.

Counter 628 is preset in response to each HCLR pulse to a count readfrom look up table 626 which, in turn, is determined by the duration ofthe line interval being read from the memory, as represented by the datastored in latch circuit 602. Counter 628 counts the clock pulsessupplied by clock generator 606, and when a first count, identified ascount A, is reached, counter 628 applies a signal to flip-flop circuit630 to set this flip-flop circuit. As a result, the flip-flop circuitproduces the output signal HDSP, shown in FIG. 7C. Counter 628 continuesto count the clock pulses supplied thereto; and when count B is reached,flip-flop circuit 630 is reset. From FIG. 7C, it is seen that signalHDSP is of a rectangular waveform whose positive portion coincides withthe useful video information provided in a horizontal line interval. Thedelay between pulse HCLR and the positive portion of signal HDSP is afunction of the count to which counter 628 is preset; and this, in turn,corresponds to the start read time and is determined by the profilepattern.

Signal HDSP is combined with the output VID from flip-flop circuit 622in AND gate 624. The AND gate produces a series of pulses each of awidth equal to the positive portion of the signal HDSP, and the periodof the output signal UNDSP from AND gate 624 is defined by the positiveportion of the signal VID (FIG. 7F). The signal UNDSP is used to enablethe read-out cycle of the memory.

Whereas FIG. 6 is a block diagram of timing circuitry used to enable theread-out operation of the memory when the vertical period is changed byvarying the durations of the horizontal line intervals, FIG. 8 is ablock diagram of timing circuitry used to enable the memory readoperation when the vertical period is adjusted by adding or deletinglines from a field. The timing circuitry illustrated in FIG. 8 includeslatch circuits 802, 804 and 814, comparators 806 and 816, counter 808,flip-flop circuit 810 and an AND gate 812. Latch circuits 802 and 804are similar to latch circuits 618 and 620 and are adapted to store theline counts identifying the top line and bottom line, respectively, ofthe displayed video picture.

Latch circuits 802 and 804 are coupled to comparator 806 which, in turn,is coupled to counter 808, the latter being adapted to count HCLR pulsesof the type shown in FIG. 7B. The output of comparator 806 is coupled toflip-flop circuit 810 whose output is, in turn, coupled to AND gate 812.It is appreciated that the combination of latch circuits 802 and 804,comparator 806, counter 808, flip-flop circuit 810 and AND gate 812 aresimilar to and perform substantially the same function as latch circuits618 and 620, comparator 616, counter 614, flip-flop circuit 622 and ANDgate 624, described above in connection with FIG. 6.

The output of counter 808 also is coupled to comparator 816 which isadapted to compare the count of this counter with a line number countstored in latch circuit 814. This line number count identifies the lastraster line in a video picture read out from the memory (e.g. line#241). It is appreciated that the same number of active video lines(e.g. 220 lines) is read from the memory, whether the vertical period isincreased or decreased. Of course, the number of "black" line intervalsthat precede and follow the active line intervals is modified, asdetermined by processor 110 which controls synchronizing signalgenerator 116 accordingly, (FIG. 1).

The HCLR pulses supplied to counter 808 may be derived from the actualhorizontal synchronizing pulses included in the video signal or,alternatively, a counter similar to counter 604 may be used to generatethe HCLR pulse periodically. In this instance, since the duration ofeach line interval is fixed at the standard duration of 63.56microseconds, there is no need to modify the count to which the counterwould be preset.

Counter 808 is similar to counter 614 in that the count produced therebyrepresents the vertical line count. As successive line intervals areread from the memory, counter 808 is incremented. When the vertical linecount reaches the number of the last active line included in the field,comparator 816 produces an UNEND output to reset the counter.

Comparator 806 toggles flip-flop circuit 810 to produce the VID signalshown in FIG. 7F, and this VID signal is combined with the HDSP signal(FIG. 7C) to produce the UNDSP signal. As mentioned above, signal UNDSPenables the read operation of the memory.

As described herein, the present invention controls the vertical periodof a television signal either by adjusting the duration of thehorizontal line intervals included in each field of the televisionsignal or by adding or deleting line intervals from the field. Themodified television signal whose vertical period thus is changed may betransmitted directly via conventional "over-the-air" broadcastingtechniques, by cable techniques or by subscription televisiontechniques. A television receiver which is supplied with this modifiedtelevision signal nevertheless is able to display an adequate videopicture in response thereto. However, if this modified television signalis recorded by conventional VTR's, the change in vertical periodinhibits those VTR's from accurately recording and reproducing thetelevision signal, thus preventing an adequate video picture from beingreproduced. The modified television signal thus may be thought of as aviewable but non-recordable video signal.

The present invention also may be used in a subscription televisiondistribution network of the type shown in FIG. 9. Typically, televisionsignals are distributed to subscribers by way of, for example, cable, inan encoded or scrambled format. When such a subscription televisiondistribution network is used with the present invention, it is preferredto supply to the cable distribution site, also known as the head end, atelevision signal having standard vertical intervals but including datawhich represents the profile pattern to be used at the head end forchanging the vertical intervals in the manner described above. Ofcourse, if desired, the television signal supplied to the head end maybe modified by having its vertical period varied in the manner discussedabove (i.e. the television signal will exhibit non-standard verticalintervals).

In addition, it is desirable that so-called "fingerprint" indicia beadded to the television signal at the head end so that if anunauthorized copy somehow is made, that copy will include the"fingerprint" which, typically, identifies the time of transmission, thecable distribution site and the operator of that site. Of course, finalencoding or scrambling of the television signal is effected at the cabledistribution site.

When the present invention is used in the subscription televisionnetwork shown in FIG. 9, the source of the television signal, that is,the television programming, preferably is reproduced from a preparedvideo tape by a VTR 902. The television signal reproduced from the VTRis supplied to a scene change detector and a fingerprint locationdetector 904. The scene change detector has been described above; andthe fingerprint location detector is adapted to sense a location in thetelevision signal at which fingerprint data should be inserted prior todistribution to subscribers. One embodiment of a fingerprint locationdetector which may be included in subsystem 904 is illustrated in FIG.10. Essentially, the fingerprint location detector senses a substantialmodification in the video signal of one line with respect to thenext-following line in a field. It has been found that if fingerprintdata, typically, a single bit, is inserted into the active video signalat this location, its presence is not perceived in the video picture.The fingerprint location detector functions to determine this location.

Scene change detector and fingerprint location detector 904 supplysignals to produce a video and time code record 906. The video and timecode record may comprise a video recording in which both the compositetelevision signals and the time codes which identify the respectiveframes in the composite television signals are recorded.

In addition, a record, such as a magnetic disk, is made of theparticular frames in which scene changes are detected and properlocations for insertion of fingerprint data are found. This recordpreferably is comprised of time code data to identify the frame in whicha scene change occurs, and also a numerical count to identify theparticular horizontal line interval and segment of that line interval inwhich fingerprint data may be inserted.

A controller 910 responds to the video time code record 906 and also tothe scene change time code and fingerprint location 908 to select aprofile pattern, as discussed above. In addition, any geometriccorrection that may be needed in the video signal, such as the geometriccorrection discussed with reference to FIG. 5, also is made bycontroller 910. Still further, the composite television signal, whichhas not yet been subjected to vertical period adjustments, may betransmitted to the aforementioned head end at the cable distributionsite in scrambled format. Such scrambling provides security againstunauthorized reception of the composite television signal which, but forthe scrambling, would be in condition to be recorded and reproduced. Onepreferred technique for scrambling the composite television signal is torearrange the line intervals in each field. Of course, informationidentifying the rearrangement, that is, a so-called "scramble map" isproduced; and this scramble map, together with profile data representingthe selected profile pattern and fingerprint location data are insertedinto any suitable location of the television signal, such as thevertical blanking interval (VBI). It is recognized that several lineintervals included in the VBI are not used for useful information; andit is convenient to insert the profile data, scramble map andfingerprint location data in one or more of these VBI line intervals.Preferably, the profile data, scramble map and fingerprint location data(referred to, for simplification, merely as VBI data) are encryptedprior to insertion. In one embodiment, a conventional DES encryptiontechnique may be used. Finally, controller 910 scrambles the televisionsignal in accordance with the scramble map inserted into the VBI. Ofcourse, this data may be inserted into other locations of the televisionsignal, such as is the horizontal blanking intervals, one bit of data ata time.

The output of controller 910 is represented as video, VBI data and timecode 912. The time code information represents the location of eachframe in the scrambled television signal; and at this stage in thesignal processing, the VBI data is comprised of the aforementionedencrypted profile data, scramble map and fingerprint location data. Inone embodiment, a scrambled master distribution tape containing video,time code and VBI data is prepared. This master video tape may bephysically delivered to a VTR 918 located at the head end of the cabledistribution site or, alternatively, information recorded on thescrambled master distribution tape simply may be reproduced andtransmitted, such as via satellite transmission, from the location ofcontroller 910 to the head end at the cable distribution site.Conventional uplink 914 and downlink 916 are provided to accommodatesuch satellite transmission.

At head end 920, vertical period adjustments to the composite televisionsignal are made, in accordance with the present invention. Of course, asmentioned previously, such vertical period adjustments may be made priorto receipt of the television signal by the head end. In addition, thescrambled video signal is descrambled in accordance with the scrambledata map which, in turn, is decrypted and used to control thedescrambling operation. Furthermore, the fingerprint location dataencrypted prior to insertion into the television signal, also isdecrypted and used to identify the proper locations in the video signalin which suitable fingerprint data may be inserted. It is expected thatthe resultant, modified television signal (i. e. the television signalwhose vertical period has been changed in accordance with the presentinvention) then is encoded in accordance with the encoding techniqueadopted by the cable distribution network. The encoded televisionsignal, containing fingerprint data and having its vertical periodmodified as aforementioned then is transmitted via the cabledistribution network. Alternatively, the encoded, modified compositetelevision signal may be transmitted by other means to an electronictheater.

Referring to FIG. 10, a logic diagram representing the manner in whichthe fingerprint location is detected is illustrated. As mentioned above,fingerprint data is inserted into the active video portion of atelevision signal at a location in a field whereat a sudden change invideo characteristics from one line to the next occurs. Comparator 1002and delay circuit 1004 detects a sudden increase in, for example,luminance level. The comparator is supplied with the incoming videosignal at one input thereof and also as supplied with the preceding lineof that video signal via delay circuit 1004, identified as a 1H delaycircuit. It is seen that delay circuit 1004 delays the incoming videosignal by a duration equal to a horizonal line interval. Although notshown, an attenuator may be used to supply the incoming video signal tocomparator 1002 such that an output is produced by the comparator onlyif the incoming video signal exceeds the delayed version of that videosignal by a factor equal to the attenuation factor. In one embodiment,this attenuation factor is on the order of about 4. Alternatively anamplifier may be used to amplify the delayed video signal supplied tothe comparator. In any event, the video and delayed video signalssupplied to the comparator may be as illustrated in FIGS. 11A and 11B,wherein FIG. 11A represents a sudden increase in the luminance level inthe field interval presently being received. FIG. 11C illustrates theoutput of comparator 1002.

Preferably, only one location in a field interval has fingerprint datainserted thereinto. AND gate 1006 is coupled to comparator 1002 to makecertain that the output of the comparator is gated only once during afield interval. As will be explained, a flip-flop circuit 1020 is resetby a strobe pulse STB2, produced by, for example, a microprocessor, atthe end of a field interval. The flip-flop circuit thus remains resetonly until comparator 1002 produces its output (FIG. 11C) and then theflip-flop circuit is set at a suitable delayed time thereafter. AND gate1006 is conditioned to pass the output of comparator 1002 when flip-flopcircuit 1020 exhibits its reset state.

Another constraint on detecting the location at which fingerprint datais to be inserted is that this location should not be present during thehorizontal blanking interval. Accordingly, end gate 1006 is providedwith an inverted version of a horizontal blanking pulse such that theAND gate is inhibited during horizontal blanking intervals.

The output of comparator 1002 is used to initially reset a flip-flopcircuit 1008, and the output of AND gate 1006 triggers this flip-flopcircuit to its set state in coincidence with a clock pulse supplied to aclock input of the flip-flop circuit by a suitable clock generator. Inthe illustrated embodiment, clock pulses on the order of 250 KHz aresupplied to flip-flop circuit 1008. As is also shown, this flip-flopcircuit preferably comprises a D-type flip-flop, with the output of ANDgate 1006 coupled to the data input D thereof. It is recognized that, byreason of the timing of the 250 KHz clock pulses, flip-flop circuit 1008always will be reset in response to the output of comparator 1002 justslightly in advance of being set by this same output as passed throughAND gate 1006. The output signal, designated DIFF, produced by flip-flopcircuit 1008 is illustrated in FIG. 11D.

This DIFF signal is supplied to a flip-flop circuit 1010 which normallyis in its reset state awaiting this DIFF signal. In the illustratedembodiment, flip-flop circuit 1010 comprises a D-type flip-flop, withthe DIFF signal supplied to the data input D and with 250 KHz clockpulses supplied to the clock input thereof. FIG. 11E illustrates theoutput of flip-flop circuit 1010, and it is seen that the output signalproduced by this flip-flop circuit, designated fingerprint locationFPINT, is delayed relative to the DIFF signal. It will be appreciatedthat this delay is equal to a cycle of the 250 KHz clock pulse.

Also not shown, the FPINT signal is supplied to the microprocessormentioned above, and in response to this FPINT signal, themicroprocessor returns a strobe signal STB1 to reset the flip-flopcircuit. FIG. 11F illustrates the relative timing of this strobe signalSTB1, and in one embodiment, the microprocessor returns the strobesignal STB1 at the completion of the line interval in which the FPINTsignal is produced. Thus, flip-flop circuit 1010 will be reset to awaitthe occurrence of the next DIFF signal.

As also shown in FIG. 10, the FPINT signal sets flip-flop circuit 1020,thereby inhibiting AND gate 1006 until the flip-flop circuit next isreset. Consequently, one and only one output of comparator 1002 ispassed by the AND gate, notwithstanding the possibility that severalsuccessive outputs may be produced by the comparator during a fieldinterval. Of course, and as mentioned above, flip-flop circuit 1020 isreset by the STB2 pulse produced by the microprocessor at the end of thefield interval in which the FPINT signal had been produced. Thus,flip-flop circuit 1020 may be set once and only once during a fieldinterval.

The FPINT signal produced by flip-flop circuit 1010 is coupled to theload input of a latch circuit 1012 to enable the latch circuit toreceive and store the contents of counter 1014 coupled thereto. Counter1014 counts horizontal blanking pulses HZBLNK and, thus, the count ofthis counter identifies the number of the horizontal line interval thenbeing received. As illustrated, the counter is cleared, or reset, inresponse to the vertical blanking pulse normally produced once duringeach field interval. Accordingly, latch circuit 1012 stores therein thenumber of the horizontal line interval in which the FPINT signal isproduced. This is used to identify the number of the line interval inwhich fingerprint data is to be inserted. This line number is suppliedto the microprocessor, and the microprocessor clears the latch circuitby supplying signal STB1 thereto, thereby conditioning the latch circuitto store the line number of the horizontal line interval in the nextfield interval at which fingerprint data is to be inserted.

Similarly, the FPINT signal is supplied to the load input of latchcircuit 1016 to enable this latch circuit to store therein the countthen reached by counter 1018. Counter 1018 is cleared, or reset, at thebeginning of each horizontal line interval in response to the horizontalblanking pulse HZBLNK. The counter then counts the 250 KHz clock pulsesto provide a count representing a particular location or segment of aline interval. As an example, fifteen of these clock pulses may beproduced during each horizontal line interval, and the count reached bycounter 1018 at the time that the FPINT signal is produced representsthat segmented location in the line interval (whose number wasidentified by the count now stored in latch circuit 1012) at whichfingerprint data may be inserted. Thus, the counts stored in latchcircuits 1012 and 1016 identify the particular line interval in a fieldinterval and also the segment in that line interval at which fingerprintdata is to be inserted. As shown in FIG. 9, this data representing theinsert location for fingerprint data is stored for subsequentintroduction into the VBI data.

FIG. 12 is a functional block diagram of controller 910 shown in FIG. 9.The apparatus of FIG. 12 includes a VTR 1201 for reproducing the videosignal whose vertical period is to be modified in accordance with thepresent invention and which will be scrambled prior to transmission orother delivery to the cable distribution site. The locations in eachvertical interval of this video signal at which fingerprint data is tobe inserted also is identified.

The video signal is played back by VTR 1201 while being re-recorded onVTR 1211 and monitored on a video monitor 1209 by a supervisor 1213.This playback and monitoring operation is used to select appropriateprofile patterns which best fit this video signal (as discussed above),and profile data representing such profile patterns is inserted into theVBI data. Accordingly, as a video signal is played back by VTR 1201,time code reader 1203 supplies to a computer 1207 time codesrepresenting each of the played back frames. Also, a synchronizingsignal separator 1205 detects the vertical interval and supplies data tothe computer corresponding thereto. It is recalled that the particularframes in which scene changes occurred had been determined by scenechange detector 904 (FIG. 9), and the location in each field in whichfingerprint data may be inserted also have been detected. Such frameidentifications of scene change and fingerprint locations are stored on,for example, a magnetic disk 1219, and this stored information issupplied by a disk interface 1217 to computer 1207. The computer nowutilizes the previously obtained scene change and fingerprint locationdata with the time code information supplied by time code reader 1203 toproduce a record for every vertical blanking interval. This recordidentifies the particular location of the profile pattern for each framereproduced by VTR 1201 (and identified by time code reader 1203) andalso identifies the number of the line interval in the field intervaland segment of that line in which fingerprint data may be inserted.Still further, computer 1207 generates a scramble map (discussed above)to identify the particular scramble rearrangement that will be used fora field. Thus, computer 1207 generates for each field of the videosignal, the following information profile data representing the verticalperiod for that field in accordance with the present location along theprofile pattern, fingerprint location data and scramble mapping data.This information is stored in suitable data record format and isarranged as a VBI data record for insertion into predetermined locationsof the television signal (such as the vertical blanking interval in eachfield). Advantageously, all of this VBI data is encrypted such as inaccordance with a DES encryption code, described above, ad the encryptedVBI data is inserted into the video signal. This video signal containingthe encrypted VBI data is recorded on VTR 1211 and distributed, eitherby physically transporting the recorded tape to the cable networkdistribution site or playing back this recorded tape for reception atthe cable network distribution site.

FIGS. 13A-13C represent the vertical blanking interval and VBI datainserted thereinto, in accordance with a preferred embodiment. Asmentioned previously, one technique that may be used to scramble thevideo data is to randomly rearrange groups of lines of a field interval.For example, if 240 active lines in a field are contained in theviewable portion, or raster, of the video picture, these 240 lines arebroken up into, for example, 4 different blocks, each block of adifferent length. As a numerical example, one block may be formed of 8line intervals, another block may be formed of 150 line intervals, yetanother may be formed of 45 line intervals and the last block may beformed of 37 line intervals. These blocks of different lengths arerearranged, thus resulting in a scrambled television signal. Continuingwith this numerical example, let it be assumed that a field memory isformed of at least 256 rows, each row being adapted to store a lineinterval and of course, there will be extra "spare" rows in the fieldmemory.

Consistent with the numerical example discussed above, to scramble thetelevision signal, the first block of 8 line intervals is stored in, forexample, memory rows 141-148. The second block of 150 line intervals isstored in memory rows 186-335. The third block of 45 line intervals isstored in memory rows 95-140 and the fourth block of 37 line intervalsis stored in memory rows 149-185. If the memory rows are read out insequential order, the television signal is scrambled because blocks 1,2, 3 and 4 would be transmitted as blocks 3, 1, 4 and 2, respectively.

FIG. 13A is a waveform diagram representing a typical vertical blankinginterval included in a field interval of an NTSC television signal. Asshown, the vertical blanking interval includes a first set of equalizingpulses followed by a set of vertical synchronizing pulses followed byanother set of equalizing pulses. Then, a number of "blank" fieldintervals follows and these "intervals" are, in turn, followed by lineintervals containing active video information. Two available lineintervals included in the vertical blanking interval are used to storethe VBI data. FIGS. 13B and 13C represent these two line intervalswhich, as an example, may be any desired line intervals between lines 10and 20 in the field interval.

FIG. 13B represents six bytes of VBI data representing the scramble map,and FIG. 13C represents six bytes of VBI data, two bytes beingassociated with the remainder of the scramble map, two bytes identifyingthe location in which fingerprint data may be inserted, one bytecontaining profile data and a "spare" byte. The scramble map identifiesthe number of line intervals included in each of the aforementioned fourblocks and also the number of the first line included in each block.Stated otherwise, the scramble map identifies the number of memory rowsused to store each block of scrambled line intervals, and also thenumber of the first row in each block. Thus, in FIG. 13B byte 0identifies a count of 8 line intervals included in the first block, andbyte 1 identifies memory row 141 as the first row in which 8 line blockis stored. Byte 2 represents a count of 150 line intervals included inthe second block, and byte 3 identifies memory row 186 as the first rowin which this block is stored. Byte 4 represents a count of 45 lineintervals, and byte 5 identifies memory row 95 as the first row in whichthis block is stored.

Continuing with FIG. 13C, byte 0 represents a count of 37 line intervalsand byte 1 identifies memory row 149 as the first row in which thisblock of line intervals is stored. Byte 2 identifies the line in thisfield interval in which fingerprint data may be inserted, and byte 3identifies the particular segment of this line interval in which thatfingerprint data is inserted. Byte 4 contains profile data and, inaccordance with the two embodiments of the present invention describedherein, this byte may represent the duration of the first 20 lineintervals included in this vertical field, or the byte may represent thenumber of lines included in the field. As byte 4 changes, the verticalperiod of the field interval correspondingly changes.

In one embodiment, each vertical blanking interval in each field may beprovided with the VBI data shown in FIGS. 13B and 13C. In analternative, the VBI data may be inserted into the vertical blankinginterval of only the first (i.e. the odd) field of each frame. Those ofordinary in the art will appreciate other variations which may be usedto accommodate the VBI data shown in FIGS. 13B and 13C.

The manner in which the VBI data that is generated by computer 1207(FIG. 12) having the format discussed above (FIGS. 13B and 13C) isinserted into a vertical blanking interval now will be described withreference to FIG. 14. As illustrated, VBI data is inserted into atelevision signal by VBI data insertion circuit 1402. This circuit issupplied with a signal from VBI timing circuit 1404 to indicate thepresence of the vertical blanking interval in the incoming televisionsignal. The VBI timing circuit is supplied with horizontal synchronizingpulses, as may be recovered from the incoming television signal, todetermine when the vertical blanking interval occurs. For example, theVBI timing circuit may include a simple counter for counting thehorizontal synchronizing pulses.

VBI data insertion circuit 1402 is supplied with the fingerprintlocation data from, for example, the circuit shown in FIG. 10, profiledata as may be produced by processor 110 (FIG. 1) or as may be producedby controller 910 (FIG. 9), and the scramble map as may be produced by,for example, computer 1207 (FIG. 12) and represented by the variousbytes discussed above with respect to FIGS. 13B and 13C. In theembodiment shown in FIG. 14, the fingerprint location data, profile dataand scramble map are extracted from data written into a field databuffer 1408 by computer 1406. Computer 1406 may be the same computer asaforementioned computer 1207 (FIG. 12) and is adapted to derive frommagnetic disk 1221 the data which had been compiled previously. Forexample, computer 1406 may read from magnetic disk 1221 and store infield data buffer 1408 the following information: the number of eachfield interval (or frame), as may be determined from the time code datasupplied to computer 1207 as each frame is reproduced from VTR 1201, thefingerprint location data produced by the circuitry shown in FIG. 10, aprofile data corresponding to the desired profile pattern selected fromprofile library 118 (FIG. 1) and the scramble map consistent with adesired scramble format (e.g. the number and size of each block of lineintervals to be scrambled).

The aforementioned data stored in field data buffer 1408 is compiled foreach field interval of the incoming television signal. In the embodimentshown in FIG. 12, the incoming television signal is reproduced by VTR1201, and the field data buffer thus contains the time code data,fingerprint location data, profile data and scramble map for eachreproduced field (or frame).

For convenience, the fingerprint location data stored in field databuffer 1408 is supplied to a fingerprint location data buffer 1410.Also, the profile data stored in field data buffer 1408 is supplied toprofile data buffer 1412. Finally, each scramble map stored in fielddata buffer 408 is supplied to scramble map buffer 1414. Theserespective buffers supply the data stored therein to VBI data insertioncircuit 1402 whereat the data is assembled in the format shown in FIGS.13B and 13C and inserted into the proper line intervals included in thevertical blanking interval of the incoming television signal.

In one embodiment, a new accumulation of data is loaded into field databuffer 1408 with each new field interval read from the VTR. In analternative embodiment, field data buffer 1408 may include severalstages adapted to store the time code data, fingerprint location data,profile data and scramble map for several field intervals, and computer1406 may load into the field data buffer this information associatedwith each of those respective field intervals.

A decoder 1416 functions to separate the active video information fromthe incoming television signal and supplies this information to A/Dconverter 1418 which digitizes the video information. As an example, 900pixels for each line interval may be produced by the A/D converter andsupplied to memory 1420 for storage therein. In one embodiment, memory1420 comprises a dual memory adapted to store odd and even fields, andthus designated a "dual" memory. As one field of digitized videoinformation is loaded into memory 1420, a previously stored fieldtherein may be unloaded and supplied to a D/A converter 1424 forcombination in mixer 1426 with the synchronizing pulses, verticalblanking interval, black inactive line intervals and VBI data suppliedby VBI data insertion circuit 1402. Memory address control 1422 selectsthe appropriate memory included in dual memory 1420 into which digitizedline intervals are written and from which those digitized line intervalsare read. Memory address control 1422 also determines the write-in andread-out rates for the dual memory which, for the embodiment shown inFIG. 14, are synchronized with the "standard" horizontal synchronizingsignal. The memory address control also determines the particular rowsin which the line intervals are stored, as determined by the scramblemap read from scramble map buffer 1414. The output from mixer 1426,which comprises the scrambled composite television signal containing theVBI data discussed above, is recorded on VTR 1428.

VBI data insertion circuit 1402 additionally functions to encrypt thefingerprint, profile and scramble map data prior to insertion in thetelevision signal (such as in the vertical blanking interval). Asmentioned above, it is preferred to use a DES encryption key for suchencoding.

In the embodiment shown in FIG. 14, the television signal recorded byVTR 1428 corresponds to the television signal provided by circuit 912(FIG. 9). It is appreciated, therefore, that the vertical period of thistelevision signal constitutes the standard vertical period of 16.683milliseconds. Changes in the vertical period, that is, modification ofthe television signal to prevent it from being accurately reproduced ifit subsequently is recorded on a conventional VTR, is carried out by theapparatus shown in FIG. 15 which, it will be appreciated, incorporatesthe present invention discussed previously with respect to FIGS. 1 and5.

The apparatus shown in FIG. 15 is located at the head end, or cablenetwork distribution site. The purpose of this apparatus is to modifythe vertical period of the television signal, as discussed in detailhereinabove, and to permit fingerprint data to be inserted into theidentified location of the active video signal. An incoming televisionsignal whose vertical blanking interval has been prepared in accordancewith the apparatus shown in FIG. 14 and which has been scrambled, isreceived either by means of, for example, satellite transmission, or byreproducing same from a video tape (as represented by VTR 1503). Ineither event, the scrambled and VBI-encoded television signal is assumedto be present in NTSC format and is converted by NTSC-to-RGB decoder1505 to separate red, green and blue video components, each componentbeing scrambled as aforesaid.

The usual 3.58 MHz color subcarrier burst signal and horizontalsynchronizing signals are recovered from the incoming television signal,and the subcarrier and horizontal synchronizing signals are supplied totiming generator 1507 whereat suitable timing pulses re generated tocontrol the timing of portions of the remaining illustrated circuitry.As an example, a timing signal frequency of six times the colorsubcarrier frequency f_(s) is generated, as is a timing signal whosefrequency is 3f_(s).

These timing signals are supplied to memory load control circuit 1511and to memory unload circuit 1513 which operate to load memory 1519 withdigitized line intervals of the separated R, G and B components of thetelevision signal, and also to unload the memory so as to adjust thevertical period thereof in accordance with the present invention, and todescramble the incoming television signal.

A vertical interval detector 1518 detects the presence of the verticalblanking interval in each field of incoming television signal; and thisdetector may be located either upstream or downstream of the NTSC-to-RBGdecoder. In any event, the vertical interval detector serves to stripthe vertical blanking interval from the incoming television signal andsupply it to VBI data detector 1509. The VBI data detector receivestiming pulses from timing generator 1507 for the purpose of separatingfrom the incoming vertical blanking interval the encrypted fingerprint,profile and scramble map data. This separated VBI data is supplied to acentral processing unit (CPU) 1515, together with a suitable DESdecryption key. It is recognized that, of course, the purpose of the DESdecryption key is to permit the proper decoding of the encrypted VBIdata.

CPU 1515 also is coupled to memory load control circuit 1511 and tomemory unload control circuit 1513 to select the particular field memoryincluded in memory 1519 for loading, to select the particular fieldmemory for unloading, to descramble the incoming line intervals so as torestore the proper order thereto, and to control the manner in whichtelevision data is read out from the selected field memory. It is thislatter feature which results in a modification of the television signalby adjusting the vertical period thereof. Thus, CPU 1515 controls memoryunload control circuit 1513 so as to determine the read-out rate foreach line interval read from memory 1519. In the other embodimentdescribed herein, CPU 1515 controls memory unload control circuit 1513so as to determine the read-out time of line intervals read from memory1519 and the number of black line intervals to be added to the activelines read from the memory, as described above. By changing the read-outrate of memory 1519, the duration of the line intervals read therefromlikewise is changed. Also, by changing the number of line intervalsincluded in each field, the duration of each field and, thus, theduration of each frame may be adjusted.

Of course, the particular read-out rate used to unload memory 1519, orthe number of inactive lines to be included in a field, is determined bythe profile data included in the vertical blanking interval of theincoming television signal. The manner in which CPU 1515 operates tocontrol the vertical period in accordance with the selected profilepattern has been discussed in detail hereinabove and need not berepeated here.

The separated R, G and B video components are digitized by separate R, Gand B A/D converters 1517. Thus, and in the manner discussed above, eachA/D converter produces a line interval of pixels, each pixel having avalue representing the chrominance level of that component. A/Dconverters 1517 supply the R, G and B digitized line intervals toseparate R, G and B field memory devices 1519. It is preferred that eachfield memory device be comprised of eight separate field memories, fourfield memories to accommodate four odd fields and four field memories toaccommodate four even fields. Memory 1519 thus may be formed oftwenty-four separate memory units, eight memory units for each of the R,G and B components, with each set of eight memory units being adapted toaccommodate four frames, each frame being formed of two interlaced oddand even field intervals.

The scramble map received in a vertical blanking interval is decrypted,and each such scramble map represents the scrambled order of the lineintervals included in the next-following field. Consistent with theexample described above, the first block of line intervals is stored inrows 141-148, and these rows are read out from memory 1519,line-by-line, first. Then, rows 186-335 are read out, line-by-line,constituting the second block of line intervals. Following row 335, rows95-140 are read from the memory 1519, and it is recalled that these rowsconstitute the third block of line intervals. Finally, rows 149-185 ofmemory 1519 are read out, and these rows comprise the fourth block ofline intervals. Thus, notwithstanding the receipt of a scrambled fieldinterval, the scramble map recovered from the vertical blanking intervaland stored in CPU 1515 serves to descramble the vertical fieldintervals, thereby recovering the video signal in proper order.

As each line interval of pixels is read from a field memory included inmemory 1519, the pixels are converted into analog form by D/A converter1521. In the preferred embodiment wherein separate R, G and B memorydevices are used as memory 1519, D/A converter 1521 likewise is formedof separate R, G and B, D/A converters. Thus, each chrominance componentis recovered in analog form, and these recovered analog signals, havingtheir vertical periods modified in accordance with the presentinvention, are supplied to RGB-to-NTSC encoder 1525 for combining the R,G and B components into an NTSC color video signal.

The output of the RGB-to-NTSC encoder is supplied to a cabledistribution head end unit 1527 for mixing with the usual horizontalsynchronizing pulses, vertical blanking pulses and color subcarrierbursts.

As a result, a conventional NTSC composite television signal, having theusual synchronizing and color bursts added thereto, but having modifiedvertical periods is supplied to the cable network.

FIG. 16 illustrates in somewhat greater detail the manner in whichtiming generator 1507 and memory load control circuit 1511 operate toload memory 1519 with received, scrambled video signals. As before, theincoming video signal is supplied to NTSC-to-RGB decoder 1505 which, inturn, supplies separated R, G and B video components to A/D converters1517. It is recalled from FIG. 15 that the A/D converters supply memory1519 with digitized line intervals for each of the R, G and Bcomponents.

The incoming video signal also is supplied to a synchronizing signalseparator 1602 which separates from the incoming video signal thehorizontal synchronizing pulses. A color subcarrier recovery circuit1604 also is supplied with the incoming video signal and recoverstherefrom the usual color subcarrier of frequency f_(s). A frequencymultiplier 1606 multiplies the recovered color subcarrier by factors of3 and 6, respectively, thereby producing timing signals of frequencies3f_(s) and 6f_(s), respectively. These timing signals, together with theseparated horizontal synchronizing pulses, are supplied to a phasegenerator 1608 which, in turn, generates the HCLR pulses (such asdiscussed above with respect to FIG. 7B) together with three phasedtiming signals identified as PHA, PHB and PHC, respectively, thefrequency of each of these timing signals being equal to 3f_(s), butthese signals exhibiting relative phase shifts of 120° with respect toeach other. The HCLR signal, which coincides approximately with therecovered horizontal synchronizing pulses, is counted by a counter 1612,the count of which represents the vertical line count. Thus, the countof counter 1612 indicates the raster line number then being received bythe illustrated apparatus.

The recovered horizontal synchronizing signals also are supplied to aline analyzer 1610 together with a horizontal count signal the latterbeing represented as an 8-bit digital signal. This HCNT signalrepresents the present horizontal position of the line interval includedin the video signal then being received. Line analyzer 1610 generates aLDEND signal which occurs generally at the first equalizing pulseincluded in a vertical field. Thus, the LDEND signal may be used toindicate the start of a field interval and serves to reset counter 1612,thus resetting the vertical line count at the beginning of the lineintervals commencing in the vertical blanking interval. Counter 1612thus accurately tracks the line intervals as they are received.

The HCNT signal produced by counter 1614 is supplied to a decoder 1616which utilizes the HCNT signal to produce a horizontal display signalHDSP. This HDSP signal is similar to that shown in FIG. 7C, andrepresents that portion of each line interval wherein active videoinformation is present. It will be recognized that this HDSP signal isused to control memory 1519 so as to effectively "open" the memory toreceive digitized line interval information only during the activeportion of that interval.

VBI detector 1620 is coupled to A/D converter 1517 and is adapted todetect and pass the VBI data to serial-to-parallel converter 1624. TheVBI detector is enabled by VBI line decoder 1622 which, in turn,responds to the vertical line count generated by counter 1612. Thus,during those line intervals in which VBI data has been inserted, forexample, during the selected line intervals between lines 10 and 20 of afield interval, decoder 1622 enables VBI detector 1620 to pass the VBIdata which is present in those line intervals. As a result, fingerprintlocation, profile and scramble map data are converted from serial form(i. e. the form in which they are present in the vertical blankinginterval) to parallel form, and this data then is stored in latchcircuit 1626 to be supplied thereafter to CPU 1515. If desired, thelatch circuit may include separate stages, each stage storing arespective one of the fingerprint location data, the profile data andthe scramble map. As determined by CPU 1515, this data may betransferred thereto as called for by the CPU.

As mentioned above, the scramble map data present in a vertical blankinginterval represents the scramble map for the next-following fieldinterval. Of course, this scramble map data is transferred to CPU 1515by latch circuit 1626, and then, prior to the receipt of thenext-following field interval, the CPU supplies latch circuit 1630 witha count representing the number of lines included in the first block ofscrambled video data that will be received in the next-following fieldinterval. At the same time, the CPU supplies to latch circuit 1634 acount representing the address of the first row in memory 1519 in whichthe first line interval of the first block of scrambled video data is tobe stored, or loaded. Thus, the starting row in which the first block ofscrambled video information is to be stored, as well as the size of thatblock are loaded into latch circuits 1634 and 1630, respectively. Thecounts stored in these latch circuits then preset counters which, inturn, supply addresses to memory 1519 to address the proper rows thereininto which the received and digitized line intervals are loaded. Asshown, counter 1632 is coupled to latch circuit 1630 and counter 1636 iscoupled to latch circuit 1634. Both of these counters count the HCLRpulses generated by phase generator 1608 so as to provide current,updated addresses for the memory.

In one embodiment, counter 1632 is decremented such that theinstantaneous count thereof indicates the number of line intervalsremaining in the block of scrambled line intervals being received.Preferably, counter 1636 is incremented so as to address successive rowsin memory 1519 into which each received line of digitized videoinformation is stored. In the numerical example discussed above, thevideo information is received in the following order: block 3,consisting of 45 line intervals, followed by block 1, consisting of 8line intervals, followed by block 4 consisting of 37 line intervals,followed by block 2 consisting of 150 line intervals. CPU 1515 utilizesthe scramble map supplied thereto by latch circuit 1626 such that, whenblock 3 is received, counter 1632 is preset to a count of 45 and counter1636 is preset to a count of, for example, 178. When counter 1632 isdecremented to a count of 0, counter 1636 will be incremented to a countof 222. Then, counter 1632 is preset to a count of 8 and counter 1636 ispreset to a count of 20. Block 1 next is received, and this block isstored in rows 20-27, respectively, of memory 1519. When all rows ofthis block is received, counter 1632 will have been decremented to acount of 0, whereafter this counter is preset to a count of 37 andcounter 1636 is preset to a count of 223. Block 4 next is received andis stored at rows 223-259, respectively, in memory 1519. When the lastrow of this block is received, counter 1632 will have been decrementedto a count of 0, and the CPU then presets counter 1632, via latchcircuit 1630, to a count of 150. At this time, counter 1636 is preset toa count of 28; and block 2 is stored, line-by-line, at rows 28-177,respectively, in memory 1519. Thus, the scrambled video information isdescrambled and stored, in order, at the proper row addresses of memory1519. The contents of this memory then may be read out in the mannerdiscussed above so as to change the vertical period of each fieldinterval, in accordance with the present invention.

In one embodiment of this invention, memory 1519 is comprised of dynamicrandom access memories (DRAM) which, as is known to those of ordinaryskill in the art, are relatively inexpensive but operate at a relativelyslow rate. Moreover, a DRAM must be refreshed periodically to accuratelyretain the digital information stored therein. In one embodiment, theoperating cycle of a typical DRAM may be too slow to accommodate thesampling rate at which the A/D converters operate. For example, if theA/D converter samples the incoming R, G and B components at a rate equalto the color subcarrier frequency f_(s), or at a rate equal to 3 timesthis frequency, the operating speed of a typical DRAM may not besufficient to accommodate this sampling rate. It is for this purposethat phase generator 1608 (FIG. 16) generates the three phased timingpulses PHA, PHB and PHC, respectively One embodiment of one field memoryusing such a DRAM, but timed to load and unload R, G and B components,respectively, is illustrated in FIG. 17. This embodiment represents acompromise, whereby the operations of the DRAM are divided into threephases so that the speed limitations of the individual DRAM devices areovercome by phase overlapping. The illustrated one field of memoryactually is comprised of nine DRAM devices, one for each phase and onefor each of the R, G and B color components.

The illustrated DRAM devices 1711-1731 are known as "single port"devices wherein the same terminal, or pin, functions both as an inputand an output. Memory devices 1711, 1713 and 1715 are used to store onefield of the red component, memory devices 1719, 1721 and 1723 are usedto store one field of the green component, and memory devices 1727, 1729and 1731 are used to store one field of the blue component. The R, G andB color components are derived from the incoming television signal byNTSC-to-RGB decoder 1701. Separate R, G and B A/D converters 1703, 1705and 1707 digitize each line interval of the respective color components,and 8-bit pixel values are supplied to the R, G and B latch circuits1709, 1717 and 1725, respectively. The timing signal 3f_(s) produced bymultiplier 1606 (FIG. 16) is used to load successive pixels into theirrespective latch circuits.

Each memory device is addressed by a row and column address technique.Stated otherwise, each memory device may be thought of as having rows ofstorage locations for storing respective line intervals, and eachstorage location in a row may be addressed as a column address to storetherein a pixel produced by A/D converter 1703 (or 1705 or 1707). Inaddition to addressing a row and column of the memory device, eachmemory device also is provided with a write enable input which, whensupplied with a write control signal enables a pixel to be written intothe location addressed by the row and column addresses. A clockgenerator 1735 generates row and column addresses, together with a writecontrol signal, all supplied to memory device 1711. Similarly, clockgenerator 1737 generates row and column addresses and a write controlsignal for memory device 1713. Finally, clock generator 1739 generatesrow and column addresses together with a write control signal for memorydevice 1715. If memory devices 1711, 1713, and 1715 are thought of asphases A, B and C for the red field memory, clock generators 1735, 1737and 1739 may be thought of as the phase A, phase B and phase C clockgenerators, respectively. These clock generators are driven by a decodermatrix 1733 which supplies the respective clock generators with timingpulses derived from the PHA, PHB and PHC signals produced by phasegenerator 1606 (FIG. 16), together with load and unload signals (whichselect the write and read memory functions, respectively) and a selectsignal (supplied by CPU 1515 (of FIG. 15) for selecting the particularfield memory which is to be loaded and unloaded.

Column address counters 1741, 1743 and 1745 are supplied with timingpulses of a frequency 3f_(s) and are used to address successive columnsin each addressed row of a corresponding phase of the memory devices. Asa numerical example, about 680 columns are addressed successively foreach row. It is recognized that column address counter 1741 addressesthe columns of phase A memory device 1711 (as well as the columns ofphase A memory device 1719 and phase A memory device 1727). Columnaddress counter 1743 addresses the columns of phase B memory device 1713(as well as the columns of phase B memory device 1721 and phase B memorydevice 1729). Finally, column address counter 1745 addresses the columnsof phase C memory device 1715 (as well as the columns of phase C memorydevice 1723 and phase C memory device 1731).

Row address counters 1747, 1749 and 1751 are supplied with the HCLRsignal and are used to address successive rows of the phase A, phase Band phase C memory devices, respectively. Thus, when a row is addressedin phase A memory device 1711 (or phase A memory device 1719 or phase Amemory device 1727), 680 successive columns in that row are addressed bycolumn address counter 1741. A similar cooperative relationship existsbetween row address counter 1749 and column address counter 1743, andbetween row address counter 1751 and column address counter 1745.

During a load operation, the select and load signals supplied to decodermatrix 1733 are used to select the field memory into which the digitizedvideo signals are to be written, as determined by CPU 1515, and latchcircuits 1709, 1717 and 1725 are enabled to supply to the selected fieldmemory the 8-bit pixels stored in each latch circuit. The write controlsignal generated by clock generators 1735, 1737 and 1739 enable thepixels to be written into the selected field memory, and the columnaddress signals generated by these clock generators serve to "clock"each pixel into the row and column location determined by the row andcolumn address counters at the particular time established by the columnaddress signal. Thus, at the phase A clock time, the pixels stored inlatch circuits 1709, 1717 and 1725 are written into the addressed rowand column location of phase A memory devices 1711, 1719 and 1727; atthe phase B clock time, the pixels then stored in latch circuits 1709,1717 and 1725 are written into the addressed row and column locations ofphase B memory devices 1713, 1721 and 1729; and at the phase C clocktime, the pixels stored in latch circuits 1709, 1717 and 1725 arewritten into the addressed row and column locations of phase C memorydevices 1715, 1723 and 1731.

During an unload, or read operation, a similar operation is carried out,except that now the unload signal supplied to decoder matrix 1733 servesto enable read-out latch circuits 1755, 1757 and 1759 to receive thepixels read from the addressed row and column locations of the phase A,phase B and phase C memory devices, at the phase A, phase B and phase Cclock times determined by the column control signals generated by clockgenerators 1735, 1737 and 1739, respectively. The contents then storedin these read-out latch circuits are supplied to D/A converts 1761, 1763and 1765, respectively, at an output timing rate equal to 3f_(s). FromFIG. 17, it is seen that the converted analog R, G and B components arecombined in NTSC encoder 1767 and supplied as a composite video signalwhose vertical period is adjusted in accordance with the memory read-outtiming that has been discussed above in conjunction with FIGS. 1 and 5.

Although not shown herein, the timing of the row and address controlsignals produced by each of clock generators 1735, 1737 and 1739functions to permit the contents of each of the phase A, phase B andphase C memory devices to be refreshed periodically, to be loaded, andto be unloaded. Since a refresh operation occurs at times other thanwhen a particular row of memory is loaded or unloaded, each row addresscounter includes a register to store temporarily the address of theparticular row which is in the process of being refreshed. In oneembodiment, the refresh operation serves to refresh 32 rows of a memorydevice during each horizontal blanking interval. Since active videoinformation is not present during the horizontal blanking interval, thisrefresh operation does not interfere with the loading and unloadingcycles of the field memories. It is appreciated, therefore, that eighthorizontal blanking intervals are needed to refresh 256 rows of videoinformation stored in each of the phase A, phase B and phase C memorydevices.

While the present invention has been particularly shown and describedwith reference to preferred embodiments, it will be readily understoodby those of ordinary skill in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe invention. This invention may be applied directly to televisionsignals which are transmitted either by over-the-air broadcasttechniques, by subscription techniques or by a cable distributionnetwork. The use of this invention in conjunction with subscriptiontelevision services, as when this invention is located at the head endof a cable distribution network, has been described. When used in atelevision subscription system, the vertical periods of the fieldintervals can be adjusted either at the head end location, as describedherein, or at any other location upstream of the head end.

It is intended that the appended claims be interpreted as includingthose modifications and changes which have been discussed throughoutthis specification, as well as equivalents thereto.

What is claimed is:
 1. A method of modifying a composite televisionsignal to inhibit reproduction of an unauthorized recording thereof byconventional video recorders but enable the display of a video picturetherefrom on a television receiver, comprising:increasing the timedurations of horizontal line intervals included in a first predeterminednumber of frames of the television signal from a standard horizontalline duration to a pre-established maximum time duration and thendecreasing said time durations from said pre-established maximum to saidstandard; decreasing the time durations of the horizontal line intervalsincluded in a second predetermined number of frames of the televisionsignal from said standard to a pre-established minimum time duration andthen increasing said time durations from said pre-established minimum tosaid standard; and limiting the increase and decrease in the timedurations of said horizontal line intervals such that the accumulatedincrease or decrease over a vertical interval is less than 200 nsec. 2.The method of claim 1 wherein said first predetermined number of framesis substantially equal to said second predetermined number of frames. 3.The method of claim 2 wherein the difference between said standardhorizontal line duration and said pre-established maximum time durationis substantially equal to the difference between said standardhorizontal line duration and said pre-established minimum time duration.4. The method of claim 1 wherein said first predetermined number offrames is substantially different from said second predetermined numberof frames.
 5. The method of claim 4 wherein the integral of theincreased time durations of the horizontal line intervals over saidfirst predetermined number of frames is substantially equal to theintegral of the decreased time durations of the horizontal lineintervals over said second predetermined number of frames.
 6. The methodof claim 5, further comprising the step of selectively determiningdesired ones of said pre-established maximum and minimum time durationsfrom a store of several pre-established time durations.
 7. The method ofclaim 1, further comprising the step of detecting a change in the sceneof the video picture represented by said television signal; and settingthe time durations of the horizontal line intervals included in theframe in which said change in scene is detected substantially equal tosaid standard horizontal line duration.
 8. The method of claim 7,further comprising the steps of selectively changing saidpre-established maximum and minimum time durations and said first andsecond predetermined numbers of frames to inhibit different types ofvideo recorders from reproducing said television signals forsatisfactory video picture display.
 9. The method of claim 1, furthercomprising the steps of encoding the modified television signal by aselected one of plural different encoding techniques; transmitting theencoded, modified television signal to authorized receiving stations;and selectively changing said pre-established maximum and/or minimumtime durations to be within operating limits of the selected encodingtechnique.
 10. The method of claim 1 wherein each step of increasing anddecreasing the time durations of the horizontal line intervals comprisesproviding a digitized representation of said horizontal line intervals;storing said digitized representations in respective addresses of anaddressable memory device; and reading out from said respectiveaddresses the digitized representations at slower read-out rates toincrease said time durations and at faster read-out rates to decreasesaid time durations, whereby said time durations exceed said standardhorizontal line duration when said read-out rates are less than apredetermined standard rate and said time durations are less than saidstandard horizontal line duration when said read-out rates exceed saidstandard rate.
 11. The method of claim 10 wherein the rate at which saiddigitized representations are read out from said respective addresses iscontrolled by profile data, said profile data determining the first andsecond predetermined numbers, the pre-established maximum and minimumtime durations and the rates at which said read-out rate increases anddecreases; and further comprising the step of selectively varying saidprofile data.
 12. The method of claim 11 further comprising the step ofgeometrically correcting the digitized representations of saidhorizontal line intervals read out from said respective addresses,whereby the first digitized representation of the horizontal lineinterval which is read out from said addressable memory devicecorresponds to the top raster line interval in a displayed video picturenotwithstanding the change in the duration of the read out horizontalline intervals from said standard horizontal line duration.
 13. Themethod of claim 12 further comprising the steps of delaying the readingout of the first digitized representation of the horizontal lineinterval from said addressable memory device when the duration of thatread out line interval is greater than standard and advancing thereading out of the first digitized representation of the horizontal lineinterval from said addressable memory device when the duration of thatread out line interval is less than standard.
 14. The method of claim 11wherein said digitized representation of said horizontal line intervalscomprises pixel values of respective pixels included in each horizontalline interval; and further comprising the steps of combining a portionof a pixel value of one horizontal line interval with a portion of anadjacent pixel value of the next horizontal line interval to produce acomposite pixel value; and storing respective horizontal line intervalsof composite pixel values.
 15. The method of claim 14 wherein said stepof combining comprises determining the percentages of the adjacent pixelvalues to be combined as a function of said profile data; and adding thedetermined percentages of adjacent pixel values to produce saidcomposite pixel value.
 16. The method of claim 15 wherein said step ofdetermining the percentages of the adjacent pixel values to be combinedcomprises storing as a look up table data representing predeterminedpercentages of predetermined pixel values, addressing said look up tableas a function of a pixel value read from said addressable memory deviceand said profile data, and reading from said look up table a percentageof the pixel value read from said addressable memory device.
 17. Themethod of claim 16 wherein said step of addressing said look up tablecomprises generating a first portion of said address in response to saidprofile data and generating a second portion of said address in responseto said pixel value read from said addressable memory device.
 18. Amethod of modifying a composite television signal to inhibit thereproduction of an unauthorized recording thereof by conventional videorecorders but enable the display of a video picture therefrom on atelevision receiver, comprising:increasing above a standard number ofhorizontal line intervals normally included in a frame the number ofhorizontal line intervals included in a first predetermined number offrames of the television signal; decreasing below said standard numberthe number of horizontal line intervals included in a secondpredetermined number of frames of the television signal; the rate atwhich the numbers of horizontal line intervals are increased anddecreased, the maximum and minimum numbers of horizontal line intervalsin a frame to which said numbers of horizontal line intervals areincreased and decreased, and the first and second predetermined numbersof frames containing the increased and decreased numbers of horizontalline intervals all corresponding to a profile pattern representingchanges with respect to time in the number of horizontal line intervalsin a frame and having a positive portion representing said firstpredetermined number of frames containing more than said standard numberof horizontal line intervals in each frame and a negative portionrepresenting said second predetermined number of frames containing lessthan said standard number of horizontal line intervals in each frame;and selectively changing said profile pattern from among a plurality ofprofile patterns and correspondingly changing at least one of thefollowing: (a) the rate at which the number of horizontal line intervalsin a frame change; (b) the maximum number of horizontal line intervalsincluded in a frame; (c) the minimum number of horizontal line intervalsincluded in a frame; (d) the first predetermined number of framescontaining more than said standard number of horizontal line intervals;and (e) the second predetermined number of frames containing less thansaid standard number of horizontal line intervals.
 19. The method ofclaim 18, further comprising the steps of detecting a change in thescene of the video picture represented by said television signal, andhaving transitions between said positive and negative portions of saidprofile pattern pass through a level corresponding to said standardnumber of horizontal line intervals substantially at detected scenechanges.
 20. The method of claim 19, further comprising the steps ofstoring profile data representing different respective profile patterns,selecting stored profile data representing a profile pattern whosetransitions through said level have a greater frequency of occurrence atdetected scene changes, and controlling the increase and decrease in thenumber of horizontal line intervals in successive frames of thetelevision signal in accordance with the selected profile data.
 21. Themethod of claim 20 wherein at least one of said stored profile datarepresents a profile pattern which, when used to control the increaseand decrease in the number of horizontal line intervals in successiveframes of the television signal results in a television signal which ifrecorded and reproduced by a conventional VTR does not result in anacceptable viewable video picture; and further comprising the step ofselecting during certain times the last-mentioned profile data.
 22. Themethod of claim 20 further comprising the step of selectively adding anoffset to the selected profile data to modify the profile patternrepresented thereby so as to increase the respective maximum and minimumnumbers of horizontal line intervals included in a frame.
 23. The methodof claim 20 further comprising the step of selectively adding an offsetto the selected profile data to modify the profile pattern representedthereby so as to decrease the respective maximum and minimum numbers ofhorizontal line intervals included in a frame.
 24. The method of claim18 further comprising the steps of digitizing at least each horizontalline interval of active video information in each frame of thetelevision signal; writing the digitized active video line intervalsinto respective storage locations of memory means; and subsequentlyreading from said memory means the digitized active video lineintervals.
 25. The method of claim 24 further comprising the steps ofdelaying the reading of the first active video line interval from saidmemory means when the profile pattern determines that the frame containssubstantially more than said standard number of line intervals; andadvancing the reading of the first active video line interval from saidmemory means when the profile pattern determines that the frame containssubstantially less than said standard number of line intervals.
 26. Themethod of claim 18 further comprising the steps of generating profiledata representing a selected profile pattern; inserting said profiledata into a predetermined portion of said television signal identifyingthe rate at which the number of horizontal line intervals are increasedand decreased, the maximum and minimum numbers of horizontal lineintervals in a frame, the number of frames included in the positiveportion of the selected profile pattern and the number of framesincluded in the negative portion of the selected profile pattern; andtransmitting the television signal having the profile data insertedtherein to a remote location whereat said profile data is recovered andused to control the increase and decrease in the number of horizontalline intervals in successive frames of the television signal to beretransmitted from said remote location.
 27. Apparatus for modifying acomposite television signal to inhibit reproduction of an unauthorizedrecording thereof by conventional video recorders but enable the displayof a video picture therefrom on a television receiver, comprising:lineduration increasing means for increasing the time durations ofhorizontal line intervals included in a first predetermined number offrames of the television signal from a standard horizontal line durationto a pre-established maximum time duration and then decreasing said timedurations from said pre-established maximum to said standard; lineduration decreasing means for decreasing the time durations of thehorizontal line intervals included in a second predetermined number offrames of the television signal from said standard to a pre-establishedminimum time duration and then increasing said time durations from saidpre-established minimum to said standard; and means for limiting theincrease and decrease in the time durations of said horizontal lineintervals such that the accumulated increase or decrease over a verticalinterval is less than 200 nsec.
 28. The apparatus of claim 27 whereinsaid first predetermined number of frames is substantially equal to saidsecond predetermined number of frames.
 29. The apparatus of claim 28wherein the difference between said standard horizontal line durationand said pre-established maximum time duration is substantially equal tothe difference between said standard horizontal line duration and saidpre-established minimum time duration.
 30. The apparatus of claim 27wherein said first predetermined number of frames is substantiallydifferent from said second predetermined number of frames.
 31. Themethod of claim 30 wherein the integral of the increased time durationsof the horizontal line intervals over said first predetermined number offrames is substantially equal to the integral of the decreased timedurations of the horizontal line intervals over said secondpredetermined number of frames.
 32. The apparatus of claim 31 furthercomprising storage means for storing data representing severalpre-established time durations; and means for reading data from saidstorage means for selectively determining desired ones of saidpre-established maximum and minimum time durations.
 33. The apparatus ofclaim 27, further comprising scene change detecting means for detectinga change in the scene of the video picture represented by saidtelevision signal; and means for setting the time durations of thehorizontal line intervals included in the frame in which said change inscene is detected substantially equal to said standard horizontal lineduration.
 34. The apparatus of claim 33, further comprising adjustmentmeans for selectively changing said pre-established maximum and minimumtime durations and said first and second predetermined numbers of framesto inhibit different types of video recorders from reproducing saidtelevision signals for satisfactory video picture display.
 35. Theapparatus of claim 27, further comprising means for encoding themodified television signal by a selected one of plural differentencoding techniques; means for transmitting the encoded, modifiedtelevision signal to authorized receiving stations; and means forselectively changing said pre-established maximum and/or minimum timedurations to be within operating limits of the selected encodingtechnique.
 36. The apparatus of claim 27 wherein each of said lineduration increasing and decreasing means comprises digitizing means forproviding a digitized representation of said horizontal line intervals;memory means for storing said digitized representations in respectiveaddresses thereof; and read-out means for reading out from saidrespective addresses the digitized representations at slower read-outrates to increase said time durations and at faster read-out rates todecrease said time durations, whereby said time durations exceed saidstandard horizontal line duration when said read-out rates are less thana predetermined standard rate and said time durations are less than saidstandard horizontal line duration when said read-out rates exceed saidstandard rate.
 37. The apparatus of claim 36 further comprising profilesupply means for supplying profile data to control the rate at whichsaid digitized representations are read out from said respectiveaddresses, said profile data determining the first and secondpredetermined numbers, the pre-established maximum and minimum timedurations and the rates at which said read-out rate increases anddecreases; said profile supply means including means for selectivelyvarying said profile data.
 38. The apparatus of claim 37 furthercomprising correction means for geometrically correcting the digitizedrepresentations of said horizontal line intervals read out from saidrespective addresses, whereby the first digitized representation of thehorizontal line interval which is read out from said memory meanscorresponds to the top raster line interval in a displayed video picturenotwithstanding the change in the duration of the read out horizontalline intervals from said standard horizontal line duration.
 39. Theapparatus of claim 38 wherein said correction means includes means fordelaying the reading of the top raster line from said memory means whenthe duration of the line intervals being read are greater than standard,and means for advancing the reading of the top raster line from saidmemory means when the duration of the line intervals being read are lessthan standard.
 40. The apparatus of claim 37 wherein said digitizingmeans includes means for generating pixels in each of the horizontalline intervals, said pixels having respective pixel values; and furthercomprising means for combining a portion of a pixel value of onehorizontal line interval with a portion of an adjacent pixel value ofthe next horizontal line interval to produce a composite pixel value;and means for replacing the pixel values in a stored horizontal lineinterval with the composite pixel values.
 41. The apparatus of claim 40wherein said means for combining comprises means for determining thepercentages of the adjacent pixel values to be combined as a function ofsaid profile data, and means for adding the determined percentages ofadjacent pixel values to produce said composite pixel value.
 42. Theapparatus of claim 41 wherein said means for determining the percentagesof the adjacent pixel values to be combined comprises look up tablemeans for storing data representing predetermined percentages ofpredetermined pixel values, table address means responsive to a pixelvalue read from said memory means and to said profile data foraddressing said look up table means, and table read means for readingfrom said look up table a percentage of the pixel value read from saidmemory means.
 43. The apparatus of claim 42 wherein said table addressmeans generates a first address portion in response to said profile dataand a second address portion in response to said pixel value read fromsaid memory means.
 44. Apparatus for modifying a composite televisionsignal to inhibit the reproduction of an unauthorized recording thereofby conventional video recorders but enable the display of a videopicture therefrom on a television receiver, comprising:line intervalincrease means for increasing above a standard number of horizontal lineintervals normally included in a frame the number of horizontal lineintervals included in a first predetermined number of frames of thetelevision signal; line interval decrease means for decreasing belowsaid standard number the number of horizontal line intervals included ina second predetermined number of frames of the television signal;profile means for providing a profile pattern representing changes withrespect to time in the number of horizontal line intervals in a frame,said profile pattern having a positive portion representing said firstpredetermined number of frames containing more than said standard numberof horizontal line intervals in each frame and a negative portionrepresenting said second predetermined number of frames containing lessthan said standard number of horizontal line intervals in each frame;means for selectively changing said profile pattern from among aplurality of profile patterns; and means for applying said profilepattern to said line interval increase and decrease means for changingat least one of the following: (a) the rate at which the number ofhorizontal line intervals in a frame change; (b) the maximum number ofhorizontal line intervals included in a frame; (c) the minimum number ofhorizontal line intervals included in a frame; (d) the firstpredetermined number of frames containing more than said standard numberof horizontal line intervals; and (e) the second predetermined number offrames containing less than said standard number of horizontal lineintervals.
 45. The apparatus of claim 44, further comprising scenechange detecting means for detecting a change in the scene of the videopicture represented by said television signal; and wherein said profilemeans provides profile patterns having transitions between said positiveand negative portions which pass through a level corresponding to saidstandard number of horizontal line intervals substantially at detectedscene changes.
 46. The apparatus of claim 45, wherein said profile meanscomprises profile storage means for storing profile data representingdifferent respective profile patterns, and selecting means coupled tosaid profile storage means for selecting stored profile datarepresenting a profile pattern whose transitions through said level havea greater frequency of occurrence at detected scene changes.
 47. Theapparatus of claim 46 wherein at least one of said stored profile datarepresents a profile pattern which, when used to control the increaseand decrease in the number of horizontal line intervals in successiveframes of the television signal results in a television signal which ifrecorded and reproduced by a conventional VTR, does not result in anacceptable viewable video picture; and wherein said selecting meansincludes means for selecting during certain times the last-mentionedprofile data.
 48. The apparatus of claim 46 wherein said profile meanscomprises offset means for selectively adding an offset to the profiledata selected from said profile storage means to modify the profilepattern represented thereby so as to increase the respective maximum andminimum numbers of horizontal line intervals included in a frame. 49.The apparatus of claim 46 wherein said profile means comprises offsetmeans for selectively adding an offset to the profile data selected fromsaid profile storage means to modify the profile pattern representedthereby so as to decrease the respective maximum and minimum numbers ofhorizontal line intervals included in a frame.
 50. The apparatus ofclaim 45 further comprising analog-to-digital converting means fordigitizing at least each horizontal line interval of active videoinformation in each frame of the television signal; memory means forstoring the active video horizontal line intervals; write means forwriting the digitized line intervals into respective storage locationsof said memory means; and read means for reading from said memory meansthe digitized active video line intervals.
 51. The apparatus of claim 50further comprising means for delaying the reading of the first activevideo line interval from said memory means when the profile patternrepresents a frame that contains substantially more than said standardnumber of line intervals; and means for advancing the reading of thefirst active video line interval from said memory means when the profilepattern represents a frame that contains substantially less than saidstandard number of line intervals.
 52. The apparatus of claim 44 whereinsaid profile means includes selecting means for generating profile datarepresenting a selected profile pattern; means for inserting saidprofile data into a predetermined portion of said television signalidentifying the rate at which the number of horizontal line intervalsare increased and decreased, the maximum and minimum numbers ofhorizontal line intervals in a frame, the number of frames included inthe positive portion of the selected profile pattern and the number offrames included in the negative portion of the selected profile pattern;and means for transmitting the television signal having the profile datainserted thereinto to a remote location whereat said profile data isrecovered and used to control the increase and decrease in the number ofhorizontal line intervals in successive frames of the television signalto be retransmitted from said remote location.
 53. Apparatus fortransmitting to subscribers a modified composite television signal whichinhibits reproduction of an unauthorized recording thereof byconventional video recorders but enables the display of a video picturetherefrom on a television receiver included in a subscription televisiondistribution system, said apparatus comprising:source means forproviding television program signals to be transmitted via saidsubscription television distribution system; fingerprint location meansfor identifying locations in the television program signals into whichfingerprint data related to the television program may be inserted andfor producing fingerprint location data indicative thereof; profile datameans for providing profile data of a profile pattern representingchanges with respect to time of the vertical periods of the televisionprogram signals; scramble means for rearranging the television programsignals to produce scrambled television signals and for producingscramble map data indicative of the rearrangement of the televisionprogram signals; means for inserting the fingerprint location data, theprofile data and the scramble map data into predetermined portions ofthe rearranged television program signals; means for supplying to saidsubscription television distribution system the rearranged televisionprogram signals having said fingerprint location data, profile data andscramble map data inserted therein; and vertical period adjustment meansresponsive to the supplied profile data for modifying the verticalperiods of the television program signals prior to transmission of thetelevision program signals to subscribers via said subscriptiontelevision distribution system, said vertical period adjustment meansincluding memory means for temporarily storing and reading outsuccessive field intervals of the scrambled television signals so as tomodify said vertical periods and for returning the rearranged scrambledtelevision signals to descrambled form.
 54. A method of modifying acomposite television signal to inhibit the reproduction of anunauthorized recording thereof by conventional video recorders butenable the display of a video picture therefrom on a televisionreceiver, comprising:digitizing each horizontal line interval of activevideo information in each frame of the television signal; writing afixed number of the digitized active video line intervals into memorymeans and subsequently reading from said memory means the fixed numberof digitized active video line intervals; converting the digitizedactive video line intervals read from said memory means to analog form;generating horizontal line intervals of nonactive video information; andadding a variable number of generated horizontal line intervals ofnonactive video information to the analog active video line intervalsread from said memory means, whereby the total number of line intervalsincluded in a frame is selectively greater than or less than a standardnumber of horizontal line intervals normally included in a frame,depending upon the number of line intervals of nonactive videoinformation added to the active video line intervals.
 55. Apparatus formodifying a composite television signal to inhibit the reproduction ofan unauthorized recording thereof by conventional video recorders butenable the display of a video picture therefrom on a televisionreceiver, comprising:means for deriving from said composite televisionsignal a fixed number of horizontal line intervals of active videoinformation in each frame of the television signal; nonactive video lineinterval generating means for generating horizontal line intervals ofnonactive video information; combining means for combining the fixednumber of active video line intervals with the nonactive video lineintervals to produce an output frame; and means for varying the numberof nonactive video line intervals which are combined with the fixednumber of active video line intervals such that the total number of lineintervals included in an output frame is selectively greater than orless than a standard number of horizontal line intervals normallyincluded in a frame, depending upon the number of nonactive video lineintervals which are combined.
 56. A method of modifying a compositetelevision signal to inhibit the reproduction of an unauthorizedrecording thereof by conventional video recorders but enable the displayof a video picture therefrom on a television receiver,comprising:increasing above a standard number of horizontal lineintervals normally included in a frame the number of horizontal lineintervals included in a first predetermined number of frames of thetelevision signal; decreasing below said standard number the number ofhorizontal line intervals included in a second predetermined number offrames of the television signal; the rate at which the numbers ofhorizontal line intervals are increased and decreased, the maximum andminimum numbers of horizontal line intervals in a frame to which saidnumbers of horizontal line intervals are increased and decreased, andthe first and second predetermined numbers of frames containing theincreased and decreased numbers of horizontal line intervals allcorresponding to a profile pattern representing changes with respect totime in the number of horizontal line intervals in a frame and having apositive portion representing said first predetermined number of framescontaining more than said standard number of horizontal line intervalsin each frame and a negative portion representing said secondpredetermined number of frames containing less than said standard numberof horizontal line intervals in each frame; selectively changing saidprofile pattern and correspondingly changing at least one of thefollowing: (a) the rate at which the number of horizontal line intervalsin a frame change; (b) the maximum number of horizontal line intervalsincluded in a frame; (c) the minimum number of horizontal line intervalsincluded in a frame; (d) the first predetermined number of framescontaining more than said standard number of horizontal line intervals;and (e) the second predetermined number of frames containing less thansaid standard number of horizontal line intervals; and compensating forvertical shift otherwise present in a video picture displayed from themodified television signal caused by said increasing and decreasing ofthe number of horizontal line intervals in said frames.
 57. Apparatusfor modifying a composite television signal to inhibit the reproductionof an unauthorized recording thereof by conventional video recorders butenable the display of a video picture therefrom on a televisionreceiver, comprising:line interval increase means for increasing above astandard number of horizontal line intervals normally included in aframe the number of horizontal line intervals included in a firstpredetermined number of frames of the television signal; line intervaldecrease means for decreasing below said standard number the number ofhorizontal line intervals included in a second predetermined number offrames of the television signal; profile means for providing a profilepattern representing changes with respect to time in the number ofhorizontal line intervals in a frame, said profile pattern having apositive portion representing said first predetermined number of framescontaining more than said standard number of horizontal line intervalsin each frame and a negative portion representing said secondpredetermined number of frames containing less than said standard numberof horizontal line intervals in each frame; means for selectivelychanging said profile pattern; means for applying said profile patternto said line interval increase and decrease means for changing at leastone of the following: (a) the rate at which the number of horizontalline intervals in a frame change; (b) the maximum number of horizontalline intervals included in a frame; (c) the minimum number of horizontalline intervals included in a frame; (d) the first predetermined numberof frames containing more than said standard number of horizontal lineintervals; and (e) the second predetermined number of frames containingless than said standard number of horizontal line intervals; and meansfor compensating for vertical shift otherwise present in a video picturedisplayed from the modified television signal caused by said increasingand decreasing of the number of horizontal line intervals in saidframes.